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Commonwealth Energy Biogas/PV Mini-GridRenewable Resources Program

Making Renewables Part of an Affordable andDiverse Electric System in California

Contract No. 500-00-036

Site Selection and Test Plan Report

Project 2.2 Enhanced Energy Recovery through Optimizationof Anaerobic Digestion and Microturbines

Task 2.2.2 Final Report

Prepared For: California Energy Commission

Public Interest Energy Research Renewables Program

Prepared By:

Bill Kitto, CH2M HILL, Santa Ana, California3 Hutton Centre Drive, Suite 200

Santa Ana, CA 92707

And

1104 Main Street, Suite 630Vancouver, WA 98660

March 26, 2004

LEGAL NOTICE

This report was prepared as a result of work sponsored by the California EnergyCommission (Commission). It does not necessarily represent the views of theCommission, its employees, or the State of California. The Commission, the State ofCalifornia, its employees, contractors, and subcontractors, make no warranty, express orimplied, and assume no legal liability for the information in this report; nor does anyparty represent that the use of this information will not infringe upon privately ownedrights. This report has not been approved or disapproved by the Commission, nor has theCommission passed upon the accuracy or adequacy of the information in this report.

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Contents

Section Page

Preface................................................................................................................................................. v

Executive Summary.................................................................................................................... ES-1

1 Introduction ......................................................................................................................... 1-11.1 Background ................................................................................................................ 1-11.2 Results of Project 1.1—Planning and Analysis...................................................... 1-11.3 Overview of Project 2.2 ............................................................................................. 1-21.4 Report Content and Organization........................................................................... 1-2

2 Enhanced Anaerobic Digestion Site Selection.............................................................. 2-12.1 Site Description .......................................................................................................... 2-1

2.1.1 City of Riverside ......................................................................................... 2-12.1.2 Potential Test Sites at the Plant................................................................. 2-12.1.3 Recommended Location ............................................................................ 2-5

2.2 Ultrasound Pilot System........................................................................................... 2-52.2.1 Introduction................................................................................................. 2-52.2.2 IWE Tec Equipment Description.............................................................. 2-52.2.3 Sonico Pilot Equipment Description........................................................ 2-62.2.4 Scope of Supply........................................................................................... 2-62.2.5 Required Ancillary Equipment................................................................. 2-7

2.3 Expanded Process Flow Diagram ........................................................................... 2-72.4 Test Plan...................................................................................................................... 2-9

2.4.1 Process Description .................................................................................... 2-92.4.2 Rationale for Test ........................................................................................ 2-92.4.3 Predicted Performance............................................................................. 2-102.4.4 Test Objectives and Technical Approach .............................................. 2-102.4.5 Test Matrix................................................................................................. 2-112.4.6 Facilities, Equipment, Instrumentation to Conduct Test .................... 2-112.4.7 Test Parameters and Procedures ............................................................ 2-122.4.8 Data Analysis Procedures ....................................................................... 2-152.4.9 Quality Assurance Procedures ...............................................................2-152.4.10 Contingency Measures............................................................................. 2-16

2.5 Existing Data Summary Table ............................................................................... 2-16

2.6 Mass and Energy Balance....................................................................................... 2-172.7 Test Recommendations and Schedule .................................................................. 2-17

3 Microturbine Gas Cleaning .............................................................................................. 3-13.1 Site Description .......................................................................................................... 3-1

3.1.1 General Map, Address, Contact Information, Plant Layout................. 3-13.1.2 Potential Sites at RP-1 ................................................................................ 3-1

3.2 Gas Cleaning Pilot System ....................................................................................... 3-1

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CONTENTS, CONTINUED

Section Page

3.2.1 Gas Drying ...................................................................................................3-3

3.2.2 H2S Removal ................................................................................................3-33.2.3 Package Siloxane Treatment System ........................................................3-3

3.3 Expanded Process Flow Diagram............................................................................3-43.4 Test Plan ......................................................................................................................3-4

3.4.1 Process Overview........................................................................................3-43.4.2 Rationale for Test ........................................................................................3-43.4.3 Predicted Performance ...............................................................................3-63.4.4 Test Objectives and Technical Approach.................................................3-63.4.5 Facilities, Equipment, Instrumentation to Conduct Test.......................3-73.4.6 Test Procedures ...........................................................................................3-83.4.7 Data Analysis Procedures ..........................................................................3-9

3.4.8 Quality Assurance Procedures................................................................3-103.4.9 Contingency Measures .............................................................................3-10

3.5 Existing Data Summary Table................................................................................3-103.6 Energy Balance .........................................................................................................3-103.7 Test Recommendations and Schedule...................................................................3-11

Appendix

RP-1 Gas Production 2002 Data

Tables

2-1 Enhanced Anaerobic Digestion Test Matrix .................................................................... 2-112-2 Baseline Solids Handling Data Collection ....................................................................... 2-132-3 Baseline Data Collection for Biogas and Co-gen System ............................................... 2-142-4 Plant Data ............................................................................................................................. 2-162-5 Enhanced Anaerobic Digestion Test Schedule................................................................ 2-183-1 Project Team Members Contact Information..................................................................... 3-23-2 Sampling Plan ...................................................................................................................... 3-113-3 Microturbine Gas Cleaning Test Schedule....................................................................... 3-14

Figures

2-1 Riverside Process Flow Schematic ...................................................................................... 2-3

2-2 City of Riverside Sewage Plant Layout .............................................................................. 2-42-3 Process Flow Diagram .......................................................................................................... 2-83-1 Location Map for RP-1 and Vicinity ................................................................................... 3-23-2 Plant Layout for IEUA RP-1 Facility................................................................................... 3-33-3 Potential Sites For Locating Test Equipment..................................................................... 3-53-4 Process Flow Diagram for Biogas Drying System ............................................................ 3-83-5 Process Flow Diagram for Biological H2S Removal System............................................ 3-83-6 Process Flow Diagram for Biogas Cleaning Package System.......................................... 3-9

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Preface

The Public Interest Energy Research (PIER) Program supports public interest energyresearch and development that will help improve the quality of life in California by bringingenvironmentally safe, affordable, and reliable energy services and products to themarketplace.

The PIER Program, managed by the California Energy Commission (Commission), annuallyawards up to $62 million to conduct the most promising public interest energy research bypartnering with Research, Development, and Demonstration (RD&D) organizations,including individuals, businesses, utilities, and public or private research institutions.

PIER funding efforts are focused on the following six RD&D program areas:

Buildings’ End-Use Energy Efficiency•

••

•

•

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Industrial/Agricultural/Water End-Use Energy EfficiencyRenewable EnergyEnvironmentally-Preferred Advanced GenerationEnergy-Related Environmental Research

Strategic Energy Research

For more information on the PIER Program, please visit the Commission’s Web site at:http://www.energy.ca.gov/research/index.html or contact the Commission’s PublicationsUnit at 916-654-5200.

For Commonwealth Program-specific information, please visithttp://www.pierminigrid.org.

What follows is a report for the California Energy Commission, Public Interest EnergyResearch Program, Contract Number 500-00-036, conducted by the Commonwealth EnergyTeam. The report is entitled Site Selection and Test Plan Report. This project contributes tothe Renewable Energy component of the PIER program.

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Executive Summary

BackgroundThe Project Prioritization Assessment, delivered under Task 1.1.10 of this PIER program,recommended prioritized sites and technologies for research testing and evaluation toadvance renewable energy. Sites for testing of technologies for enhanced anaerobicdigestion and gas cleaning for microturbines at wastewater treatment plants ranked highlyin that prioritized list.

The Process Selection Report for Wastewater Treatment Plants, delivered under Task 2.2.1 ofthis PIER program, recommended an ultrasound process for enhanced anaerobic digestionand a package of combined treatment technologies for gas cleaning, to be carried into a siteselection and test phase.

This site selection and test plan report carries forward the conclusions from the above-mentioned reports and provides specific site recommendations, further definition of theprocesses and their integration into the host facilities at the recommended sites, and testplans for the recommended processes.

Enhanced Anaerobic Digestion

Site Selection

The ultrasound process selected in Task 2.2.1 is recommended for testing at the City of

Riverside Water Quality Control Plant. A specific location on the south side of digesters #1and #2 at that plant is recommended and described on a plant layout in Section 2.1.

Process Definition and Equipment Vendors

Two vendors of ultrasound systems, IWE Tec and Sonico, were selected to provideequipment. Their scope of supply and recommended ancillary equipment for pilot testing isdescribed in Section 2.2 of this report. An expanded process flow diagram of integration intothe existing host facility is shown and discussed in Section 2.3.

Test Plans, Operating Data, and Schedule

Test plans and procedures, including equipment needed, predicted performance, and datagathering and analysis procedures, are provided in Section 2.4. Existing plant operating dataare summarized in Section 2.5. A baseline mass-energy balance for performancecomparisons of existing and new systems is discussed in Section 2.6, and a schedule fortesting that starts in February 2004 and ends in February 2005 is defined in Section 2.7.

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EXECUTIVE SUMMARY

Gas Cleaning for Microturbines

Site Selection

The gas cleaning process package selected in Task 2.2.1 is recommended for testing at theInland Empire Utilities Agency (IEUA) Regional Plant #1 (RP-1) facility. Three locationoptions for placement of equipment at that facility are discussed in Section 3.1:

Next to the existing treatment equipment (iron sponges and gas compressors) at thatfacility

•

•

•

North of digester No. 4 (the manure digester)

Close to the energy recovery building, southeast of the digesters

Process Definition and Equipment Vendors

The recommended gas cleaning processes include a refrigerated dryer for moisture removal,a biological process using bacteria for hydrogen sulfide removal, and a package siloxaneremoval system as manufactured by Applied Filter Technologies or Pioneer Air Systems.These processes are described further in Section 3.2 and expanded process flow diagramsare provided in Section 3.3.

Test Plans, Operating Data, and Schedule

Test plans and procedures, including equipment needed, predicted performance, and datagathering and analysis procedures, are provided in Section 3.4. Existing plant operating dataare summarized in Section 3.5. A baseline mass-energy balance for comparison ofperformance of existing and new systems is discussed in Section 3.6, and a schedule fortesting that starts in February 2004 and ends in December 2004 is defined in Section 3.7.

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SECTION 1

IntroductionIn June 2001, the Commonwealth Energy Team was awarded a programmatic contractunder the California Energy Commission’s Public Interest Energy Research (PIER) Program

to conduct research on strategies for making renewable energy more affordable inCalifornia. The Commonwealth Energy approach involves assessing the combined potentialof biogas and photovoltaic (PV) resources in a defined study area and identifying how theseresources could be developed in a complementary and cost-effective manner. TheCommonwealth Energy Team conducted this research in a real world setting so that thefindings could be applied elsewhere in California and thereby benefit more Californiaratepayers. The local area Commonwealth Energy selected for its renewable energy researchactivities is the Chino Basin, referred to in this report as the study area.

1.1 Background

The Chino Basin is rich in PV and biogas resources. Moreover, it is a rapidly growing areawith substantial and increasing electrical loads. The underlying goal of the CommonwealthEnergy PIER Renewables Mini-Grid Program is to identify potential Building Integrated PV(BIPV) and biogas energy projects, bring innovative technologies and business practices tothese projects, assess the benefit to the local electricity distribution system (the mini-grid),and then use the findings to develop a business model for siting cost-effective, renewableenergy projects. A description of the Commonwealth Energy PIER Program, including theresults of some of the work undertaken to date, is presented on the project Web site,http://www.pierminigrid.org.

An important element of the Commonwealth PIER Renewables Mini-Grid Program is aproject devoted to research on improving energy recovery from biogas derived from

anaerobic digestion. This project is identified as Project 2.2, “Enhanced Energy RecoveryThrough Optimization of Anaerobic Digestion and Microturbines.” The work summarizedin this report (Task 2.2.2) is the second activity of Project 2.2, and carries forward the resultsof the Process Selection Report completed for Task 2.2.1.

1.2 Results of Project 1.1—Planning and Analysis

Project 1.1 (Planning and Analysis Report) confirmed that projects and technologies for gascleaning for microturbines and enhanced digestion systems should be examined further.Also, it became clear during the research that because of high power costs, projects designedto maximize energy recovery from digesters and generation equipment are important and

potentially economical. These projects were therefore ranked highly in the ProjectPrioritization Assessment Report (Task 1.1.10). Those results were carried into Project 2.2.

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INTRODUCTION

1.3 Overview of Project 2.2

The objectives of Project 2.2 are:

Increase and optimize digester gas production through thermal hydrolysis andultrasound processes.

•

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•

•

Develop and optimize cost-effective gas cleanup systems.

Evaluate and quantify environmental benefits that result from using microturbines atsewage treatment plants.

Evaluate performance and cost during operation so sewage treatment plants havegreater certainty on cost and reliability of using microturbines.

The first task, 2.2.1, evaluated several different processes and selected an ultrasound processfor enhanced anaerobic digestion and a custom treatment package for gas cleaning formicroturbines, to be carried further to site selection and testing.

This report fulfills the scope of Task 2.2.2, which includes a report on selection of the bestsites at which to deploy the technologies and processes for enhanced anaerobic digestionand gas cleaning that were selected in Task 2.2.1. The report also provides (1) expandedprocess flow diagrams that further define the selected processes and show their integrationinto the selected host facilities, and (2) test plans for the new systems.

1.4 Report Content and Organization

This report is organized as follows:

Section 1 introduces the Commonwealth Energy program, provides background

information on the Chino Basin, presents an overview of the Commonwealth PIERproject for Enhanced Energy Recovery through Optimization of Anaerobic Digestionand Microturbines, and describes the objectives and content of this report.

Section 2 describes the selected test site for the enhanced anaerobic digestion process.Expanded process flow diagrams are presented, and process definition, test plans,recommendations and schedule are discussed.

Section 3 describes the selected test site for the microturbine gas cleaning process.Expanded process flow diagrams are presented, and process definition, test plans,recommendations and schedule are discussed.

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SECTION 2

Enhanced Anaerobic Digestion SiteSelection

This section evaluates the selected test site for the ultrasound pilot test. The ultrasoundtechnology to be tested is designed to increase the production of biogas from digestion oforganic solids. The City of Riverside is well suited to host the ultrasound pilot test.

2.1 Site Description

2.1.1 City of Riverside

The City of Riverside is the recommended location for the ultrasound pilot testing program.

The City of Riverside Water Quality Control Plant address is 5950 Acorn Street in Riverside,CA 92504. The point of contact for the testing is Stephen Schultz, Wastewater SystemsManager for the City of Riverside. The wastewater plant has two primary and secondarytreatment trains within the same site, referred to as Plant 1 and Plant 2. Currently, theprimary sludge is thickened at each plant and then pumped into a common line to thedigesters. The waste activated sludge (WAS) from the two activated sludge plants is sent toone pair of dissolved air flotation thickeners (DAFTs) from where the thickened wasteactivated sludge (TWAS) is sent to the digesters.

The wastewater treatment plant has five existing digesters, of which three will be inoperation during the test period. The pilot systems will be located south of Digesters #1 and

#2 for ease of access and to minimize the temporary piping and electrical cable lengths. TheCity of Riverside operates standard mesophilic digesters at 100°F, and the results from theultrasound pilot test will be applicable to treatment plants across California. The City ofRiverside process schematic is shown in Figure 2-1, and the plant layout is shown inFigure 2-2.

A third digester, Digester #4, is planned to be brought online in early 2004, and will be fedprimary solids and TWAS from Plant 2. Therefore, the feed to this digester may be slightlydifferent than the feed to the other digesters. In addition, Digester #4 is slightly larger thanthe other two digesters. Performance of Digester #4 will be monitored during the test as acheck on the performance of the test digesters, although it will not be a true control digester,owing to the differences between this and the other two digesters.

2.1.2 Potential Test Sites at the Plant

The City of Riverside is currently using two of its five digesters, Digesters #1 and #2(previously labeled Digesters #6 and #7). These two digesters are adjacent to each other andshare the same pump room and electrical room. They are also the closest digesters to theDAFTs that provide the TWAS feed to the digesters, and to the dewatering building.Figure 2-2 shows the location of test digesters and DAFTs. The City has been operatingthese two digesters since the 1980s and extensive background data are available for

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ENHANCED ANAEROBIC DIGESTION SITE SELECTION

performance of these digesters, which may be referred to during this test as necessary.Digesters #1 and #2 are similar in size, design, and mixing and heating equipment and havebeen in operation for the same duration. Plant data (provided in Section 2.5) show that thedigesters have similar performance, although plant staff have recommended a moredetailed evaluation of the two digesters prior to testing. The similarities between these two

digesters and the background data available make these suitable for side-by-side testing oftwo different ultrasound systems.

Three locations of the ultrasound equipment were considered. The evaluation criteriaincluded ease of supply of TWAS to the ultrasound systems, routing of the sonicated solidsfrom each system to the respective digester, piping for bypassing the ultrasound systems incase of a shutdown, and electrical hookup for the test equipment. The TWAS feed line to thedigesters is buried for most of its length, and is only accessible at the DAFT pump room, orin the digester pump room basement, where the digester feed pipe header and valvesystems are located. The three locations considered were:

Adjacent to the DAFT pump room•

•• On the north side of Digesters #1 and 2On the south side of Digesters #1 and 2

The location next to the DAFTs provided easy access to the feed TWAS line, but producedcomplications as it required routing of multiple temporary pipelines to convey sonicatedTWAS from each ultrasound system to the respective digesters, as well as bypass lines,across an onsite roadway that plant staff would need to use. This location significantlyincreased the total pipe length that would be required.

Location of the test equipment on the north side of the digesters was also considered. At thislocation, a single TWAS feed line could be installed from the DAFT pump room to theequipment, which would reduce the pipe length and access issued associated with the first

location. Alternatively, the TWAS feed to the test equipment could be connected to a Tsection on the feed header in the digester pump room basement. This avoided having to runlines across the access road, but the line from the pump room basement required routing itup the main access staircase, which could cause a potential safety issue for plant staff. Thesonicated TWAS from the test equipment to the digesters could be routed into the externaldigester mixing lines on the north side of the digesters. However, electrical connectionswould have to be routed from a control room on the opposite side of an access road.

Location of the test equipment on south side of the digesters was also considered. There isan existing electrical control room adjacent to the digester pump room on this side, whichhas spare capacity and could accommodate electrical needs of the test equipment. TheTWAS feed to the test equipment could be accessed at the same T-connection in the

basement that was considered for the above location. However, by locating the equipmenton the south side, the line could be run up an existing ladder, rather than the main accessstairway, and would not be a safety concern. There are mixing line access points on theexternal digester walls on the south side that could be used for routing the sonicated TWASinto the digesters.

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E

FIGURE 2-1

Riverside Process Flow Schematic

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FIGURE 2-2:

City of Riverside Sewage Plant Layout

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2.1.3 Recommended Location

Three potential test equipment locations were considered and discussed with the plant staff.It was clear that the third location, on the south side of Digesters #1 and #2, would be thebest in terms of maintaining access to the plant facilities, minimizing the length oftemporary piping and electrical lines, and minimizing potential health and safety issues.

2.2 Ultrasound Pilot System

2.2.1 Introduction

Different ultrasound systems and manufacturers are evaluated as part of the ProcessSelection Report. Two manufacturers, IWE Tec and Sonico, were selected to provideultrasound systems for pilot testing. This section briefly describes the technologies and theequipment to be provided by each manufacturer.

2.2.2 IWE Tec Equipment Description

The IWE Tec approach to ultrasound application for municipal sludges is based on partialtreatment of the secondary sludge stream. The premise is that, for this system, partialtreatment is the most cost-effective approach. The ultrasound system consists of individual‘cascade’ probes, each within an individual cylindrical reactor. The ‘cascade’ probe is apatented development of the common rod-shaped probe. The IWE Tec system operates atsonication times of 30 to 60 seconds. The systems are usually designed to run between 50 to75 percent of the maximum power, to provide a buffer and prevent the units from cuttingout because of power overloads. Because this ultrasound system operates close to themaximum amplitude, the operating power draw can only be varied by changing the load,which may be achieved by changing line pressure, feed flow rate, or solids concentration ofthe feed sludge. Some of the recent advances made to improve the cost-effectiveness of theIWE Tec system are:

Increase in the maximum amplitude from 25 µm to 50 µm•

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Increase in probe power, from 4 kW to potentially 16 kW. Probes over 4 kW have a newwater cooling system

Change in probe design from a single-cast piece to a two-piece probe to allow the lowerportion, which has the most wear, to be replaced more frequently, while the upperportion can be replaced less frequently

Data from IWE Tec ultrasound systems in Germany show that the older design, using 2-kW

probes at the lower amplitude range, typically provided improvements in anaerobicdigestion as follows:

Increase in volatile solids destruction of 20-25 percentIncrease in gas production of 25-30 percentImproved dewaterability of 0-5 percentage points

Actual results vary depending on digestion performance without ultrasound, digesterretention times, and the proportion of secondary solids in the digester feed.

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2.2.3 Sonico Pilot Equipment Description

The Sonico ultrasound system consists of individual ‘radial’ horns that are shaped like aring donut. The horns are mounted in series in a reactor that typically contains three or fivehorns. The reactor is designed with flanges at either end that connect to a 6-inch diameterpipe. The radial horn and reactor designs are covered by patents.

The Sonico approach to ultrasound application for municipal sludges is based on treatmentof the entire secondary sludge stream. The Sonico system operates at sonication times ofaround two seconds. Recent tests conducted by Sonico show that maintaining the desiredpower draw is key to achieving the optimal ultrasound dose and intensity. The system doesthis by adjusting amplitude and line pressure to maintain the set power draw. This preventsthe units cutting out on overload, and prevents performance dropping when changes in thesludge feed system would otherwise have reduced the power draw. The system is designedto typically run at 70 to 75 percent of the maximum amplitude, which provides buffering forchanging loads. Some of the recent advances made by Sonico to improve the cost-effectiveness of the system are:

Increase in the maximum amplitude from 12 µm to 16 µm••

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Increase in power, from 3 kW to 6 kW hornsMore cost-effective horn manufacturing processImprovements in the transducer cooling system

Data from Sonico ultrasound systems show that the older design, using 3 kW probes at thelower amplitude range, typically provided improvements in anaerobic digestion as follows:

Increase in volatile solids destruction of 30-50 percentIncrease in gas production of 30-50 percentImproved dewaterability of 0-2.5 percent

Actual results vary depending on digestion performance without ultrasound, digesterretention times, and the proportion of secondary solids in the digester feed.

2.2.4 Scope of Supply

The manufacturers will provide the ultrasound demonstration equipment as an integratedoperating system consisting of an equipment skid or container, necessary horns,transducers, generators to treat the specified TWAS flow; cooling system; flowmeter(s); twopressure sensors; interconnecting pipes, bypass line, valves, instrumentation, control panels;sample stations; and interconnecting power and control wiring and associated raceways.

The manufacturers will be responsible for designing their ultrasound demonstration system;delivering to the plant; providing installation instruction, assistance, and training for theCity of Riverside staff; commissioning; acceptance testing; and decommissioning.

The manufacturers will be responsible for acceptance testing of individual items ofequipment prior to demonstration testing. The City of Riverside will install the equipmentin accordance with the manufacturer’s requirements and will provide manpower duringstartup.

Section 2.4.6 lists the equipment provided by each manufacturer.

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2.2.5 Required Ancillary Equipment

The required ancillary system will include a 10,000-gallon TWAS holding tank with low,high, and high-high level controls to allow continuous flow through the ultrasoundequipment systems; temporary piping between the TWAS feed line, the ultrasounddemonstration systems and the digesters; TWAS progressive cavity feed pump for IWE Tec

Ultrasound train; emergency bypass line and automatic valving to prevent overflow of theTWAS holding tank by diverting the TWAS feed flow to Digesters #1 and #2; plug valves toisolate demonstration equipment from the sewage treatment plant; temporary power andcontrol cable to connect to the plant system; and digester gas flowmeters. Additionalservices and utilities that will be required include power supply; plant effluent for cooling;daily staffing and monitoring; and sampling and laboratory analysis during the testingperiod.

2.3 Expanded Process Flow Diagram

Two ultrasound supplier systems will be installed for a side-by-side comparison of the

technology. Ultrasound is most effective on the TWAS, which is harder to break down in theconventional digestion process. The test equipment will be installed on the TWAS feed tothe digesters. The TWAS feed from the DAFTs is not continuous throughout the day, as thepumps cycle on and off depending on levels in the TWAS tanks. However, as ultrasoundsystems are primarily sized on flow, it is preferable to provide a consistent feed to theultrasound systems, to maximize the use of the test units. Therefore, the test setup, as shownabove in Figure 2-3 , includes a TWAS holding tank that provides buffering and a morecontinuous flow to the ultrasound units. One ultrasound demonstration system will feeddigester #1; the other will feed digester #2. As the IWE Tec system only treats part of theflow, this unit has a bypass line through which the unsonicated portion will be routed to thedigesters. The holding tank and demonstration equipment will be located outside, on the

south side of the test digesters and temporary piping will feed the system.

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FIGURE 2-3

Process Flow Diagram

(Please see attached .pdf file)

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2.4 Test Plan

2.4.1 Process Description

A demonstration trial will be conducted to investigate the economic, practical and technical

benefits of using ultrasound to increase gas production on existing anaerobic digesters at theCity of Riverside Sewage Treatment Plant. The Sonico system will treat all the TWAS toDigester #1, with a design average sonication retention time of around two seconds. TheIWE Tec system will provide partial treatment (30 percent of TWAS flow) to Digester #2,and the remaining TWAS flow will bypass the ultrasound system. The IWE Tec systemtypically is designed for a sonication retention time of 30 seconds. Descriptions of the twoultrasound systems have been provided in Sections 1.2.1 and 1.2.2 of this report. Flow ratesto each system and the power draw of each will be monitored. Parameters that provideindications of the impact of ultrasound on the TWAS will be measured, including solubleCOD release, viscosity and microscopic analysis of cellular material.

The TWAS from each ultrasound system will mix with the primary sludge in the digester. Inall other respects the operation of the digesters will continue as usual, with the temperatureat around 100ºF. Ultrasound, through improved hydrolysis, is expected to providemeasurable improvements in digestion, including increased solids destruction, increasedgas production, and improvements in dewaterability.

As with any test that seeks to measure improvements in a process, it is vital that the baselineperformance is well established. This is even more important when comparing two differentsystems as part of a side-by-side test, where the merits of one system will be contrasted withthe merits of the other system. To ensure that both test digesters are operating under similarconditions, primary and TWAS flow rates and solids loading rates for each digester will bemonitored. In addition, the operating volumes of each digester will be checked through

tracer tests, so that the true hydraulic retention time may be calculated. The main digestionperformance parameters will be measured through volatile solids destruction, and gasproduction. Additional parameters will be monitored, to verify stability of the digestionprocess and downstream impacts such as dewaterability improvements. Section 1.4.7provides more detail on the parameters that will be monitored.

As the digester gas is used for generation of electricity through the on-site IC engines, thequality of gas, and the proportion of energy generated from the digester gas will bemonitored as part of the test process.

2.4.2 Rationale for Test

Ultrasound technology for improved anaerobic digestion was tested at laboratory scale asearly in the 1960’s. However, at that time, ultrasound generating technology was notsufficiently developed to provide a process that could cost-effectively be implemented atfull-scale. In the last five years, advances in ultrasound equipment have generated renewedinterest in this technology for hydrolysis of municipal solids. The technology provides aneasy retrofit option for existing wastewater treatment plants, and has a relatively low costcompared with options such as thermal hydrolysis. The simple installation and operation ofthis technology make it particularly attractive as a potentially cost-effective method for

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optimizing gas production at municipal plants. There are three primary suppliers withsystems developed for municipal applications, and these suppliers are continuing todevelop and optimize their equipment to improve cost-effectiveness. Most of the work todate has been conducted in Europe, and there is a need to develop this technology forapplication in the United States.

The longest-running ultrasound installation at a municipal treatment plant is around threeyears using low power probes (2 kW). Most of the work to date has been done in Europe,where conditions at municipal plants are often different from plants in the U.S., and asmentioned earlier, digester performance in Europe tends to be lower than in the U.S.

Sonico has conducted trials at Orange County Sanitation District (OCSD), and is currentlytesting the same equipment at a Los Angeles County Sanitation District plant, which is verysimilar to OCSD. The testing was done with 3 kW probes and was on a biological sludgeproduced from Pure Oxygen Activated Sludge Process. Additionally, data needs to becollected with sludges produced at air aerated sludge plants, which are the most commonbiological treatment processes in the U.S. The secondary solids from air aerated sludge

plants are more highly oxidized and the structure of the solids may be stronger. Therefore,the biogas production potential with ultrasound treatment may be different, and therequired energy input to achieve sufficient disintegration might be higher.

The presence of multiple vendors is beneficial for the market, as the suppliers are seeking toimprove life-cycle costs for their systems to be increasingly competitive. Each of the threesuppliers in the market has a very different approach to the application of their ultrasoundsystems and very different operational parameters, which make direct comparison of thesystems difficult. Testing of the different suppliers at the same site would enable such acomparison to be done for the first time, and the potential advantages of each system to beverified.

2.4.3 Predicted PerformanceAs there is no operating experience with the ultrasound equipment in California on a typicalsewage treatment plant, a conservative estimate of 20% improvement in gas productionfrom the TWAS is predicted. Electricity generation is expected to be increased as a result ofthe digested gas production improvement. As the City of Riverside will bring on line a thirddigester before the pilot test, only 2/3rds of the TWAS will be treated through theultrasound systems. It is anticipated that during the pilot test, the electricity generated bybiogas will increase by approximately 125 kW, offsetting natural gas use.

2.4.4 Test Objectives and Technical Approach

The aim of the enhanced anaerobic digestion test is to evaluate the cost-effectiveness ofusing ultrasound to increase digester gas production at sewage treatment plants. The test isbeing conducted at the City of Riverside sewage treatment plant, as this has primary andsecondary treatment processes that are typical of those found in California. Two differentultrasound systems will be tested side-by-side to compare different approaches toapplication of this technology for enhanced digestion. To achieve this, the objectives of thistest are:

Establish robust baseline performance data for the test digesters•

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Evaluate performance of two digesters, each with a different ultrasound system•• Evaluate operability of the two ultrasound systems (downtime, energy draw etc.)

2.4.5 Test Matrix

To achieve the test objectives, the test will be conducted in four phases, briefly described

below and summarized in Table 2-1.

1. Pretest Phase - During this phase, a number of checks will be carried out at the City ofRiverside sewage treatment plant, to ensure that the data collected during the test willbe robust and reliable. This includes calibration of all flowmeters (sludge flows and gasflows), evaluation of mixing systems on the test digesters, tracer tests to determinedigester operating volume, and collection of plant data for the past year.

2. Baseline Phase - During the first three months of the test, detailed baseline data will becollected with the newly calibrated instrumentation and following the test proceduresdescribed in Section 1.4.7 (excluding those relevant to the ultrasound systems).

3.Ultrasound Test Phase

- Once the two ultrasound systems are installed, the ultrasoundsystems and digesters’ performance will be monitored, as per the test proceduresdescribed in Section 1.4.7.

4. Continuation Phase – After the ultrasound systems have been shut down at the end ofphase three, the digesters will continue to be monitored for another two to three months,to follow the change in digester performance back to the baseline. This confirms thatimprovements seen during the ultrasound testing phase can truly be attributed to theuse of the equipment.

TABLE 2-1

Enhanced Anaerobic Digestion Test Matrix

Digester #1 Digester #2

Phase No UltrasoundWith SonicoUltrasound No Ultrasound

With IWE TecUltrasound

Pretest Phase 1 month - 1 month -

Baseline Phase 3 months - 3 months -

Ultrasound Phase - 6 months - 6 months

Continuation Phase 3 months - 3 months -

2.4.6 Facilities, Equipment, Instrumentation to Conduct Test

The ultrasound demonstration system will be provided as a complete, integrated, and fullyoperating system starting from inlet flanges of the TWAS feed pump and ending at inlet ofthe temporary piping to the digester, and will consist of the following subsystems:

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Complete ultrasound equipment, including but not limited to reactor chamber, horns/probes, boosters, extenders, transducers, generators, and cooling system, to treat thespecified TWAS flow to one digester.

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

One container or skid system to house the ultrasound equipment and all appurtenances,to be located outside and adjacent to the digesters.

One acoustic sound enclosure, if required.

Two pressure indicators.

Flowmeter(s) and required motorized valves (if needed) to control and protectdemonstration equipment.

Bypass line and valves to proportion flow for IWE Tec Ultrasound System

TWAS Progressive Cavity Pump for each Ultrasound train.

Interconnecting pipes, valves, and sample stations.

Instrumentation and control panel.

Interconnecting power and control wiring and raceways.

The required ancillary system will include:

A 10, 000-gallon TWAS holding tank with low, high, and high-high level controls toallow continuous flow through the ultrasound equipment systems.

Temporary piping between the TWAS feed line, the ultrasound demonstration systemsand the digesters.

Emergency bypass line to prevent overflow of the TWAS holding tank.

Isolation valves to isolate demonstration equipment from the plant.

Digester Gas Flowmeters.

Power supply, temporary power and control cable to be connected to plant system.

Daily staffing and monitoring.

Sampling and laboratory services during the testing period.

2.4.7 Test Parameters and Procedures

This section outlines the test parameters for the baseline, ultrasound and continuation

phases of the program, including solids data, biogas and electricity data and data specific tothe ultrasound systems.

Solids Handling Parameters

Table 2-2 provides the solids handling parameters that will be monitored during the test.One week prior to the start of the ultrasound systems, more intensive dewatering testsshould be conducted, by isolating each digester, to assess the difference in performance

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between them. This will then be repeated towards the end of the ultrasound phase, after thedigesters are at steady state operation and again during the continuation phase.

TABLE 2-2

Baseline Solids Handling Data Collection

Parameter

Primary SludgeTo EachDigester

TWAS ToEach Digester

Digested SludgeFrom eachDigester

DewateredCake

1 Frequency

Daily Flow (mgd)√ √ √2 daily

Quantity (wtpd) √ daily

TS (%) √ √ √2 √ 3 x week

VS (%) √ √ √2 √ 3 x week

Alkalinity (mg/l) √ √ √ 3 x week

pH √

√

√

3 x week

Viscosity √ √ 1 x month

VFA (mg/l) √ √ √ 3 x week

Ammonia (mg/l) √ 3 x week

Nitrate (mg/l) √ 3 x week

TKN (mg/l) √ √ √ √ 3 x week

Sulfate (mg/l) √ √ √ 3 x week

Temperature (°F) √ daily

Iron Salts (mg/l) √ √ daily

Polymer (lb/ton) √ √ √ daily

Capture rate (%) √ daily

Operation (hr/d) √ daily

# of Duty Units √ daily

1 Conduct 1 week of more intensive dewatering tests to characterize dewatering variability between eachdigester.

2 If bottom sludge is withdrawn from the digesters, the volume and solids should be recorded.

Biogas and Co-Generation System ParametersTable 2-3 provides the data to be collected to develop the baseline prior to installation of theultrasound systems. Gas flows, flared gas and electricity generation should be recordeddaily. Gas composition may be analyzed two to three times a week.

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TABLE 2-3

Baseline Data Collection for Biogas and Co-gen System

ParameterDigester Gas from

each digesterLandfill

GasNatural

GasTotal (entire

Co-gen) Frequency

Daily Flow (scfd) √ √ √ √ daily

Methane (%) √ √ √ √ weekly

H2S (ppm) √ √ √ √ weekly

BTU √ √ √ √ End of each phase

Daily electricity (kW) √ √ √ √ √

Daily amount Flared (scfd) √ √

Ultrasound System Parameters

During the phase when the ultrasound systems are on line, the testing described above inthe baseline section will be continued. In addition, weekly tests will be conducted for thefollowing additional parameters:

COD, soluble COD, and viscosity in an out of each ultrasound system••

•

•

•

•

•

Microscope analyses for filaments in an out of each ultrasound system

City of Riverside plant staff assistance will be required to check operation of the ultrasoundsystems. Both units will be provided with control panels for automated operation. A logsheet will be provided for once daily monitoring of the systems, which will include:

Electricity used by each ultrasound system;Daily recording of line pressure in and out of the ultrasound systems;

Number of units operational;Power draw for each unit; andFlow rate through the two ultrasound systems

Test Procedures

The parameters listed in Table 2-2 and Table 2-3 will be measured using existing plantequipment and sample procedures. Flow measurements will be made with existing solidsflow and gas flowmeters, which will be calibrated before the start of the test, and will becross-checked with strap-on flowmeters. The flowmeters will be checked every six monthsduring the test. Chemical data for the digester feed and exit sludges and biogas will beconducted using the standard methods for laboratory analysis of the listed parameters.

Tests that the City of Riverside laboratory is not certified to conduct will be sent to acertified external laboratory.

Digester temperature measurements will be taken from on-line temperature sensors on thedigester recirculation lines, with additional daily manual readings, as currently done byplant staff. Iron salt addition and dewatering polymer use will be calculated from the vol-umes and concentration of chemicals used, as currently monitored at the plant. Dewateringcapture rate will be calculated from solids measurements in the feed biosolids and in the

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filtrate. The hours of operation and number of dewatering units in use will be recorded byplant staff, and cross-checked with digested biosolids flows to the dewatering facility.

Ultrasound operating parameters will be recorded by the plant staff in a daily operating log,using meters installed on the two systems. Chemical and microscope analyses of thesonicated TWAS will be conducted by the City of Riverside laboratory, or by a certified

external laboratory.

2.4.8 Data Analysis Procedures

A detailed procedure will be developed to analyze the extracted data during the testingphases. This will include development of a daily log sheet for recording operationalparameters of the ultrasound units and digesters. Information from the log sheets will be ina format that can be easily input into an Excel spreadsheet. On-line data collected by theplant, such as flow rates, and laboratory data will input into Excel spreadsheets. Dataanalysis will consist primarily of monitoring trends in digester performance (volatile solidsreduction, biogas production - quality and quantity) using daily data, as well as movingaverages to provide long term trends. In addition to the digester performance, thedewaterability of the biosolids will be documented and the energy demand of theultrasound system will be documented. Data will be updated and reviewed at least everytwo weeks, as the laboratory analysis data becomes available.

Another excel spreadsheet will be created with the raw data and the calculations todetermine the operational cost for each ultrasound pilot system.

2.4.9 Quality Assurance Procedures

There are two important aspects with experimental quality assurance and control. The firstis the assurance of good sample collection and shipping methods. The appropriate samplecollection points and collection times will be demonstrated to the plant operators. The

samples will be collected by the operators in appropriate bottles provided by the laboratorythat will be conducting the tests. For samples sent to an external laboratory, the samplebottles should be stored on ice and shipped in coolers on the same day if possible, or before10:00 a.m. the next morning for samples taken later in the day. When same day shipping isnot possible (usually weekends and evenings), the sample bottles will be preserved, stored(usually at 4°C) and shipped the next morning to ensure that the appropriate proceduresand holding times are met, as specified by the analytical laboratory.

The second aspect lies with the laboratory’s procedures and QA/QC methods. As thelaboratory analysis will be conducted by the Plant’s certified laboratory or by an externalcertified laboratory, the laboratory staff should be familiar with standard sample storage,

analysis and QA/QC procedures. When immediate analysis is not possible (usuallyweekends and nights), the sample bottles will be preserved, stored (usually at 4°C) anddelivered to and analyzed in accordance with appropriate procedures and holding times, asspecified by the analytical laboratory. Replicate samples and split sample analysis will beconducted occasionally to verify reliability of results.

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2.4.10 Contingency Measures

As shown on the Process Flow Diagram, a bypass line will divert the TWAS flow to thedigesters when triggered by a high level signal on TWAS holding tank or plant’s shutdown.

Sonico ultrasound unit employs redundant horns to maintain the normal operation in case

of failure of the other horns. IWE Tec will have spare horns and parts available to allowbringing the system back-on-line in the event of equipment malfunction.

The testing period will be extended up to two months (3 HRT Cycles), if the ultrasoundsunits happen to be offline for more than two weeks.

2.5 Existing Data Summary Table

Table 2-4 provides a summary of available plant operating data for January through mid-November 2003. During this period, Digesters #1 and 2 were in operation. Once Digester #4is brought online, it is anticipated that approximately one-third of the TWAS and primarysludge flows will be sent to this digester, reducing the loading rates on the current digesters,and increasing the overall retention time.

TABLE 2-4

Plant Data

Description Unit Min Max Avg

Primary Solids Flow* MGD 0.08 0.19 0.12*

PS % TS Percent 2.55 5.85 4.35

PS % VS Percent 43.82 85.57 79.89

DAF In Flow MGD 0.16 0.79 0.55

DAF Eff Flow* MGD 0.04 0.17 0.11*

DAF % TS Percent 2.99 5.62 3.74

DAF % VS Percent 63 90 78.13

Total Dig Flow* MGD 0.124 0.27072 0.23*

Dig 1 pH SU 6.94 7.81 7.49

Dig 1 VA mg/l 26 425 82

Dig 1 Alk mg/l 2,777 3,916 3,447

Dig 1 VA/Alk ratio 0.01 0.13 0.02

Dig 2 pH S.U. 7.3 7.8 7.5

Dig 2 VA mg/l 23 367 70

Dig 2 Alk mg/l 2,882 4,239 3,588

Dig 2 VA/alk ratio 0.01 0.11 0.02

Dig In % TS Percent 3.1 5.1 4.0

Dig In % VS Percent 72 86 79

AVG VS Reduction Percent 4.01 66 50

DIG 1&2 Eff % VS Percent 54 79 65

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TABLE 2-4

Plant Data

Description Unit Min Max Avg

BP In Flow MGD 0 0.43 0.23

BP In % TS Percent 1.5 2.6 2.2

BP dtpd Ton’s 0 42 21

BP wtpd Tons 0 342 171

BP CAKE % TS Percent 10.6 16.4 12.5

Dig 1 Temp Deg. C 36 41 39

Dig 2 Temp Deg. C 36 41 39

Dig Detention Days 12 26 14

Combined Dig H2S ppm 25 111 73

Landfill Gas H2S ppm 6 91 10

Total H2S LBS/Day 1.340 6.877 3.523

Landfill Gas H2S LBS/Day 0 3 0.6

2.6 Mass and Energy Balance

As part of the baseline test phase, a mass and energy balance will be conducted to ensurethat the data being collected are robust. The energy balance will reflect planned operationalchanges at the plant, including use of a third digester and addition of polymer to the DAFTsto increase thickness of the TWAS.

2.7 Test Recommendations and Schedule

The test recommendation is to proceed with side-by-side evaluation of two differentultrasound systems for enhanced biogas production at the City of Riverside sewagetreatment plant. The two systems will be installed on Digesters #1 and 2, which arecurrently the only two digesters in operation. A pretest phase will be conducted to verifyaccuracy of on-site equipment and ensure the digesters are operated under similarconditions and loads. This will be followed by the baseline phase, with the digestersoperated under similar conditions as the ultrasound testing phase. It is necessary thatDigester #4 be operational prior to the start of the baseline phase. The ultrasound testingphase will be followed by a continuation phase, to track the return of the digesters to pre-ultrasound performance once the units are turned off. Table 2-5 summarizes the schedulefor the four phases.

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TABLE 2-5

Enhanced Anaerobic Digestion Test Schedule

Phase Duration Date

Pretest Phase 1 month April 2004

Baseline Phase 3 months May – July 2004

Ultrasound Phase 6 months August 2004– January2005

Continuation Phase 3 months February – April 2005

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SECTION 3

Microturbine Gas CleaningThe purpose of the microturbine gas cleaning pilot test is to collect and analyze data fordifferent technologies to determine their efficacy in removing hydrogen sulfide and

siloxane. This section discusses the pilot testing site location, the technologies to be tested,the process flow diagram, the testing plan, and the test recommendations and schedule.

The biogas used for operating microturbines must meet stringent quality requirements(maximum of 150 parts per million [ppm] moisture, 25 ppm hydrogen sulfide [H2S], and 10ppbv siloxanes) to prevent early deterioration of the microturbines. The biogas produced inthe digesters at a wastewater treatment plant is typically saturated and containsapproximately 500 to 2,000 ppm H2S, and 2 to 5 ppm siloxane. Biogas from manuredigestion is also saturated, contains approximately 500 to 2,000 ppm H2S and typically nosiloxanes. The content of each of these contaminants needs to be decreased to meet thebiogas quality stated above.

3.1 Site Description

The IEUA has microturbines at RP-1. RP-1 is located toward the center of the mini-grid andhas seven anaerobic digesters, an iron sponge system to remove H2S, biogas compressorsand storage, an energy recovery building, a waste gas burner, and eight microturbines. Sixof the seven digesters at RP-1 process the solids from municipal waste. Digester No. 4 isused to process dairy manure.

The RP-1 facility has been selected to conduct the biogas cleaning pilot test program becauseit has microturbines and biogas generated using both municipal waste and manure. Tocontrol H2S in the biogas from digestion of municipal waste, iron salts are being added at

the Headworks to minimize H2S formation during digestion. The biogas is further treatedusing an iron sponge. There is no siloxane removal for the internal combustion engines, butcarbon filters are used to reduce H2S levels in the biogas used in microturbines. The biogasproduced from manure typically is saturated and has high H2S concentration, but istypically free of siloxanes. To reduce H2S levels in the manure digester biogas, iron salt isadded directly to the digesters and the biogas is further treated through an iron sponge.

3.1.1 General Map, Address, Contact Information, Plant Layout

The selected site, RP-1, is located at 2450 E. Philadelphia, Ontario, CA, 91761. Figure 3-1contains RP-1 location and vicinity maps. The main contacts for the Biogas Cleaning PilotTest Program are listed in Table 3-1.

Figure 3-2 contains the overall plant layout for RP-1. This layout shows the location of theexisting digesters (northwest quadrant of the site); iron sponges, gas compressors and gasstorage (southeast of the digesters) and microturbines (north of the Control Building).

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MICROTURBINE GAS CLEANING

FIGURE 3-1

Location Maps for RP-1 and Vicinity

The push-pin indicates the location of RP-1.

Location Map

Vicinity Map

TABLE 3-1

Project Team Members Contact Information

Name Company Address Telephone Fax E-mail

Eliza Jane Whitman 909-993-1685 [email protected]

Ryan GrossIEUA

6075 Kimball AveChino, CA 91710 909-993-1699

[email protected]

Bill KittoCH2M HILL

825 NE Multnomah,Suite 1300, Portland,OR 97232

[email protected]

Fred Soroushian 714-435-6232 714-424-6232 [email protected]

Carmen Quan CH2M HILL

3 Hutton Centre Dr.,

Suite 200, Santa Ana, CA 91707 714-435-6117 714-424-2063 [email protected]

3-2 USR040230003.DOC

mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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FIGURE 3-2

Plant Layout for IEUA RP-1 Facility


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3.1.2 Potential Sites at RP-1

Figure 3-3 shows the sites for locating the test pilot equipment. These sites are identified asA, B and C. Site A is located next to the existing iron sponges and gas compressors, whichmakes it suitable for installing the pilot test equipment for the gas drying system. The mainbiogas header is buried west of the Energy Recovery Building and becomes exposed (aboveground) south of the iron sponges. The gas compressors are located only a few feet north ofthe iron sponges and the exposed main biogas header with low levels of H2S and highpressure is located East of the compressors and easily available for tapping and feeding thegas drying pilot test equipment. The location of utilities in the area will require furtherinvestigation.

Site B is located north of digester No. 4 (the manure digester). The H2S removal pilot testequipment could be located in this area to test the H2S removal efficiency. This location hasnumber of advantages. One advantage is that digester No. 4 is isolated from the H2Spretreatment system at RP-1, which consists of injecting ferric chloride at the Headworks.The H2S pretreatment is required to reduce the content of H2S in the biogas to comply with

the emissions established by the South Coast Air Quality Management District (SCAQMD).Digester No. 4 has a dedicated ferric chloride injection system that can be turned on and offwithout affecting the rest of the biogas quality. Another advantage is that the biogasproduced in digester No. 4 is from 100 percent manure digestion and contains high H2Scontent (once the iron salt addition to the digester is stopped).

Site C is located close to the energy recovery building, south-east of the digesters. This site issuitable for installing the packaged siloxane treatment system. The existing biogas headerfeeding the existing microturbines is located near site C. This header could be isolated fromthe existing system to allow operating the existing microturbines with the cleaned biogasfrom the packaged system.

3.2 Gas Cleaning Pilot System

The treatment process at RP-1 includes ferric chloride injection at the headwork to controlthe H2S concentration in the biogas produced at anaerobic digesters No. 1 through 3 and 5through 7. The amount of H2S in the biogas from these digesters is less than 100 ppm. Ferricchloride is directly injected into digester No. 4 to maintain the amount of H2S in the biogasat an average of 60 ppm. After the biogas is collected from all the digesters, it is treated withiron sponges to further reduce the amount of H2S to approximately 5 ppm. The biogascompressors are located downstream of the iron sponges and increase the biogas pressure to40 pounds per square inch gauge (psig) before it is stored in the biogas storage system.From the storage system the biogas is distributed to the engine generators, boilers and the

microturbines.

The proposed Gas Cleaning Pilot System consists of testing technologies that have thepotential to remove moisture, siloxanes and H2S; but that are neither being used in the USAnor have been applied at the scale needed for microturbine gas treatment. Thesetechnologies are gas drying, biological H2S removal system and a package system forsiloxane treatment. The proposed Gas Cleaning Pilot System equipment is described in thenext sections.

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FIGURE 3-3

Potential Sites for Locating Test Equipment


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3.2.1 Gas Drying

The selected technology for pilot testing is a refrigerated dryer for moisture removal and itseffects on siloxane removal through the condensate.

The refrigerated dryer system is skid mounted, suitable to handle biogas and consists of a

refrigeration unit, a vertical heat exchanger and a control. The heat exchanger moduleutilizes a plate-to-plate precooler that lowers the refrigeration energy requirements. Thisunit performs 3 functions, gas chilling, moisture separation, and condensate removal. Theunit is suitable to handle pressurized biogas between 20 and 300 psig. It handles biogas withan inlet temperature of 150 degrees F and cools it to 40 degrees F dew point. The pressuredrop across the unit is 2 psig. The unit has a Class 1, Division 1 classification. The controlpanel is explosion-proof rated.

The refrigerated dryer for this pilot test program will be sized to treat 50 standard cubic feetper minute (scfm) of biogas. This is enough biogas to run four of the existing 30-kWmicroturbines (12 scfm per microturbine).

3.2.2 H2S Removal

The H2S found in biogas can be removed through a biological process by bacteria. Thebacteria in this process oxidizes the sulfide to produce both elementary sulfur and sulfuracid. The bacteria live naturally in nearly all substrates (soil, water, sludge and manure) andrequire nutrients, oxygen/air, and humidity to live. The biological activity is temperature

dependent, and this process works more efficiently at a temperature of approximately 35°C(95°F).

The biogas flows from the digester to the H2S removal tank, which is partially filled withplastic or ceramic filter chips as growing media for the bacteria. The filter chips aresupported by grating at the tank’s bottom. The removal tank also contains a mixture of

water and nutrient solution (N, P, and K with micronutrients), which is recirculated andsprayed over the media. Artificial addition of substrate to the system is typically notrequired because the bacteria enter the process tank with the biogas. Air is also added to thebiogas to provide the required oxygen for the bacteria. Since biogas/air mixtures with over10 percent oxygen are combustible or explosive, less than 10% air is added to the biogas. Forsafety reasons, the oxygen (O2) concentration and pH are continuously measured andtransmitted to the computer control system. The tank is provided with drain and overflownozzles (one each) to remove the surplus fluid.

The system for the pilot test will be sized to treat up to 100 scfm at 1,500 ppm H2S with turndown to 50 scfm at 500 ppm H2S content.

3.2.3 Package Siloxane Treatment System

There are two companies that manufacture packaged systems to clean biogas. Applied FilterTechnology offers the SAGPack series. These are customized units designed and built tomatch specific biogas cleaning requirements. These systems can include any combination ofcompression, chilling, condensing/coalescing, siloxane removal, organic sulfur removal,desiccation, and particulate filters.

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The other company is Pioneer Air Systems, Inc. The gas drying unit in the Pioneer systemconsists of cyclic refrigeration capable of achieving an outlet temperature of –20 degrees F.The removal of siloxanes in the Pioneer system depends on liquid condensation (byadsorption with the condensed water) and polishing with activated carbon.

Both these companies will be contacted to determine if a unit can be rented or obtained for a

low capital cost. If available, the unit will be tested and used to compare technologies forsiloxane removal.

The package system for this pilot test program will be sized to treat 50 scfm of biogas, whichis enough to run 4 of the existing 30-kW microturbines at RP-1.

3.3 Expanded Process Flow Diagram

Figures 3-4 and 3-5 contain the process flow diagram for the gas drying system andbiological H2S removal system, respectively. These diagrams include the major componentsand instrumentation required for each of pilot test units. Figure 3-6 contains the process

flow diagram for the package system.

3.4 Test Plan

3.4.1 Process Overview

As part of the Public Interest Energy Research (PIER) Program, a demonstration trial will beconducted to investigate the economic, practical and technical benefits of microturbine gastreatment technologies for removing moisture, siloxane and H2S.

The gas drying system for moisture removal will be installed downstream of the existinggas compressors and will be physically located east of the existing gas compressors and iron

sponges. The biological H2S removal system will be installed north of digester No. 4 and thistechnology will be compared to the existing chemical H2S removal system using ferricchloride. The packaged siloxane treatment system will be located south-east of the digesters,close to the energy recovery building. The pilot test equipment will be installed outdoorsand temporary piping will feed each of the systems.

3.4.2 Rationale for Test

Use of biogas in microturbines requires removal of moisture, H2S, and siloxane. Most of thegas treatment technologies currently in use are either too costly or not available at the scaleneeded for microturbines. Some technologies could potentially remove multiplecontaminants from biogas. For example, moisture removal through refrigeration also allowscondensation of the siloxanes in the biogas. This removal efficiency needs to be investigatedto determine if using refrigerated gas drying would significantly reduce the size of therequired siloxane removal system.

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FIGURE 3-4

Process Flow Diagram for Biogas Drying System

CONDENSATESAMPLE POINT

BIOGAS REFRIGERATED DRYER

BIOGAS

FROM EXST

GAS

COMPRESSORS

DRIED

BIOGAS

TO

HEADER

PI TI PI TI

SAMPLE

POINT

SAMPLE

POINT

REFRIGERATION

CIRCUIT

FIQ

FIGURE 3-5

Process Flow Diagram for Biological H2S Removal System

BIOLOGICAL H2S REMOVAL SYSTEM

H2S REMOVAL

TANK

CONDENSATE

SAMPLE POINT

WATER

SUPPLY

BIOGAS

FROM

DIGESTER No. 4

H2S-

REDUCED

BIOGAS

TO

BIOGAS

HEADER

PI TI PI TI

SAMPLE

POINT

SAMPLE

POINT

RECIRC PUMP

BLOWER

NPK

NUTRIENTS

S

S

CONDENSER

/ DRYER

TODISPOSAL

FIQ

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FIGURE 3-6

Process Flow Diagram for Biogas Cleaning Package System

BIOGAS GAS CLEANING PACKAGE

SYSTEM

GAS COOLING

MODULE

SILOXANE

REMOVAL

MODULE

BIOGAS

FROM EXST

GAS

COMPRESSORS

CLEANED

BIOGAS

TO

MICRO

TURBINES

CONDENSATE

SAMPLE POINT

PI TI PI TI

SAMPLE

POINT

SAMPLE

POINT

SAMPLE

POINT

FIQ

Current technologies for H2S removal require either chemical feed (i.e., iron salts) or mediareplacement (i.e., iron sponge), which typically result in high operating costs. Localexperience in operating the biological H2S removal system (level of difficulty andoperational labor requirements) needs to be acquired and documented to analyze thissystem. This is also the case for the packaged siloxane removal system.

The proposed technologies (refrigerated dryer and biological H2S removal) for this pilot testprogram have the potential of substantially reducing the gas treatment cost. However, theavailable data for these systems is not comprehensive to allow analysis of their efficiency orcost effectiveness.

The purpose of the Digester Gas Cleaning Pilot Test program is to collect the necessaryinformation to determine the removal efficiency and cost effectiveness of these technologies.

3.4.3 Predicted Performance

The expected removal performance for the proposed technologies is based on availableempirical data.

Experimental data shows that existing biogas cleaning units can reduce H2S concentration

by 90 percent–99 percent. This means that an H2S concentration in the 2,000 ppm rangebefore treatment can be reduced to lower than 20 ppm after treatment. Bench scale testingfor siloxane removal using refrigeration and condensation, indicate a reduction of over50 percent of the siloxane concentration.

3.4.4 Test Objectives and Technical Approach

There are 2 main test objectives for this pilot program. One of them is to obtain thenecessary data to determine the contaminant removal efficiency for each of the technologies.

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The other is to obtain the necessary data to determine the cost effectiveness of operatingeach of these technologies.

The pilot test equipment and system design will include sample ports and instrument portsto facilitate the collection of samples and measuring of parameters necessary to achieve thegoals of this program. Before starting the design of the digester cleaning pilot test system, it

will be necessary to analyze the composition of the biogas in the main header and inDigester No. 4. This is required to optimize the size of the pilot test equipment.

For the gas drying system, samples of the biogas will be taken upstream and downstream ofthe refrigerated dryer once a week. These samples will be sent to the laboratory to test themoisture and siloxane content in the biogas samples and the results recorded. Samples ofthe condensate will also be collected once a week and sent to the laboratory to test itscomposition and pH and the results will be recorded. Condensate testing will help indetermining the alternatives for its disposal. In addition, the pressure and temperature ofthe biogas and the power consumed by the refrigerated dryer will be recorded daily. Aflowmeter with a totalizer will be provided upstream of the gas drying system to measure

and record the biogas flow daily. The daily amount of condensate will also be measured andrecorded.

The influent and effluent pipes of the biological H2S treatment system will be provided withports to collect biogas samples once a week. These samples will be sent to the lab to test theH2S content in the biogas and the results recorded. The temperature and pressure of thebiogas and the amount of air supplied to the system will be recorded daily. The amount ofpower consumed by the entire system (recirculation pump, motorized valves and the aircompressor supplying the air to the system) will be measured and recorded daily. Aflowmeter with a totalizer will also be provided upstream of the biological H2S treatmentsystem to measure and record the biogas flow daily.

The packaged siloxane treatment system pilot unit will be furnished with ports upstreamand downstream of each of its main elements to collect samples of biogas to test themoisture and siloxanes content. If the package unit produces condensate, a sample will becollected and its composition tested, as well. These samples will be collected and send to thelaboratory once a week and the results recorded. The pressure and temperature of thebiogas and the power consumed by each of the elements in the package unit will berecorded daily. A flowmeter with a totalizer will also be provided upstream of the gasdrying system to measure and record the biogas flow daily. The daily amount of condensatewill also be measured and recorded.

3.4.5 Facilities, Equipment, Instrumentation to Conduct Test

The equipment required to collect a biogas sample is a Tedlar bag or a field test kit suppliedby the laboratory where the testing will be conducted. Each of the sample ports will requirea manual valve to fill the biogas container for the sample. A request for proposal will be sentto laboratories with the capability to test for siloxanes, moisture, H2S, and other commonbiogas constituents. The laboratory to conduct the biogas testing for this pilot program willbe selected based on the technical merits and cost included in the submitted proposals.

A power meter with totalizer will be used to measure the electricity consumed by each ofthe systems. The reading and recording of this parameter will be done manually.

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Pressure gauges and thermowells will be used to measure the pressure and temperature ofthe biogas. The reading and recording of this parameter will be done manually.

A thermal mass flowmeter with totalizer will be used to measure the flow of biogas. Thereading and recording of this parameter will be done manually.

3.4.6 Test ProceduresBiogas testing needs to be performed once a week for each of the pilot testing equipment.The procedure will be as follows: a biogas sample will be collected at each of the sampleports (identified under Article 2.4.3) and sent to the laboratory for testing. The laboratorywill perform three primary tests—EPA TO-14 to test for volatile organics, ASTM ProcedureD-5504 GC/SCD for sulfur species, and SIL GC/MS test for individual siloxane species. Thetest results will be recorded. It is expected that the biogas samples will be collected bypersonnel from the laboratory.

For all pilot systems, the testing program also will include daily monitoring and recordingof biogas flow, temperature and pressure, and equipment power consumption.

The testing program for the gas drying and the package system will require weeklycollection and analysis of the condensate as well as recording of these results. Thecondensate from the drying equipment will be collected in a container and its volumemeasured and recorded daily. The temperature of the condensate will be measured andrecorded before disposal.

Table 3-2 contains a summary of the recommended sample collection, tests, datamonitoring, data recording, and a schedule for each.

TABLE 3–2

Sampling Plan

Sample/Parameter Monitored Test Frequency

Gas Drying System

Biogas upstream of equipment Moisture/siloxane Once a week

Biogas downstream of equipment Moisture/siloxane Once a week

Temperature -- Once a day

Pressure -- Once a day

Flow -- Once a day

System power consumption -- Once a day

Biological H2S Removal System

Biogas upstream of equipment H2S Once a week

Biogas downstream of equipment H2S Once a week



Flow -- Once a day

System power consumption -- Once a day

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TABLE 3–2

Sampling Plan

Sample/Parameter Monitored Test Frequency

Package System

Biogas upstream of equipment Siloxane Once a week

Biogas downstream of equipment Siloxane Once a week



Flow -- Once a day

Motor 1 power consumption -- Once a day

Motor 2 power consumption -- Once a day

Each of the equipment systems that will be used in this pilot testing program is providedwith its own proprietary control system for proper and safe operation. The refrigeratedsystem contains the controls for the refrigeration cycle. The packaged siloxane removalsystem is provided with controls for the condensation cycle (the siloxane removal processuses media and does not require control).

The biological H2S removal system is provided with equipment, instrumentation,appurtenances and a PLC unit to control the process. The air compressor supplying thenecessary air to the process is controlled by an oxygen sensor. If the oxygen sensor reachesthe high level setpoint, the air compressor stops operation. The pH of the fluid is alsomeasured on-line and allows water to enter the tank if the pH sensor reaches the lowsetpoint. The system is also equipped with Dräger–tubes for local measurement of H2S.

The laboratory must follow the equipment calibration recommendations to meet the ASTMand EPA requirements for the tests that are required above. Pressure gauges, thermowellsand power meters will require calibration every year. Thermal mass flowmeters will requirecalibration every 3 months.

Other data that will be collected are the cost of supplies for each system and the labor hoursdedicated to the operation and maintenance of each system. The time to inspect instrumentsand collect and record parameters will be documented separately for each system.

3.4.7 Data Analysis Procedures

The data will be input into an excel spreadsheet which will contain the necessarycalculations for the required analysis. The expected calculations are removal percentages forH2S, moisture, and siloxanes.

Another excel spreadsheet will be created with the raw data and the calculations todetermine the operational cost for each pilot system.

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3.4.8 Quality Assurance Procedures

The proposals from the laboratories will require submission of their quality assuranceprogram for sample collection and testing. As a minimum, the laboratories’ qualityassurance programs will be required to meet EPA and ASTM standard.

In the field, the collection of the condensate samples will be done using sterilized containers.Immediately after collecting the sample, the container will be labeled with the samplenumber, source, date and time.

The person performing the daily collection of data from instruments will be required to fillin the form: the area where the instruments are located, the date, and time. The order inwhich the person collects the data also will be established to ensure all readings are takenand recorded. An hour prior to collecting data, the person will be required to check theinstruments to ensure they are in working order. Repair of the non-operating instrumentswill be required prior to taking any readings.

3.4.9 Contingency Measures

The size of the biogas samples will be large enough to allow performing two of each of thethree tests required. The unused portions of the biogas samples will need to be refrigerated,in case the tests have to be performed a second time. The pilot systems will be providedwith the bypass lines to prevent disruption of plant operation in case of an equipmentmalfunction.

3.5 Existing Data Summary Table

The appendix contains the tables summarizing the monthly biogas production at RP-1.

3.6 Energy BalanceAn energy balance will be performed for each of the systems being piloted. The powerconsumed by the equipment for each of the pilot systems will be considered a parasitic loadwhen performing the energy balance for each pilot system.

For instance, for the gas drying system, the power consumed by the refrigeration unit willbe recorded and subtracted from the net energy generated by the microturbines. Theparasitic loads of the microturbines will be included in the calculation, but their effects keptseparately from that of the refrigeration value.

The same procedure will be used to calculate the energy balance for the biological H2S

removal system and the packaged system. The power consumption for the biological H2Sremoval system will be measured at the control panel and will be recorded as a totalnumber. For the packaged system, the power consumption for each motor will be recordedto allow preparing separate energy balances for each of the treatments.

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MIC

sonication retention time reference

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