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SOUTH COAST AIR QUALITY MANAGEMENT DISTRICT

Best Available Retrofit Control Technology Assessment

TXI Riverside Cement

REVISED DRAFT (Original Draft, September 19, 2006)

August 8, 2008

Engineering and Compliance

Deputy Executive Officer

Mohsen Nazemi, P.E.

Senior Manager

Brian L. Yeh

Authors: Manuel Quizon Air Quality Engineer II Marilyn Potter Air Quality Engineer II

Reviewed By: Hubert Wilson Air Quality and Compliance Supervisor

BARCT Assessment August 2008

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Table of Contents

Acknowledgement .............................................................................................................. 4 Purpose of Draft Update ..................................................................................................... 5 Executive Summary ............................................................................................................ 6 Introduction ......................................................................................................................... 6 History of Cement ............................................................................................................... 7 Cement Manufacturing Process .......................................................................................... 9

Kiln Types and Operation ............................................................................................. 10 Long Wet Kilns .......................................................................................................... 10 Dry Kilns ................................................................................................................... 10 Dry Kilns with Preheaters ........................................................................................ 11 Dry Kilns with Precalciners...................................................................................... 11

Fuels .................................................................................................................................. 11 Emissions .......................................................................................................................... 11

Thermal NOx ................................................................................................................ 12 Fuel NOx ....................................................................................................................... 12 Feed NOx ...................................................................................................................... 12 Prompt NOx .................................................................................................................. 12

Controls ............................................................................................................................. 13 Reducing NOx Formation ............................................................................................. 13

Process and Combustion Modification ..................................................................... 13 Staged Combustion Air, Indirect Firing with Low-NOx Burners ............................. 13 Secondary Combustion of Fuel ................................................................................. 15

Destroying NOx ............................................................................................................ 15 Wet Scrubbing ........................................................................................................... 15 Selective Non-Catalytic Reduction (SNCR) .............................................................. 16 Urea Injection (Dry Product) ................................................................................... 17 Selective Catalytic Reduction (SCR) ......................................................................... 17

Technology Evaluation ..................................................................................................... 18 Cost Effectiveness ............................................................................................................. 19 Analysis............................................................................................................................. 20

State Implementation Plans........................................................................................... 20 Achieved in Practice ..................................................................................................... 20 Technological Feasibility and Cost Effectiveness ........................................................ 21 Technology Transfer ..................................................................................................... 21

Case Studies for Technology Transfer ...................................................................... 21 Technology Transfer Summary ................................................................................ 23

Conclusion ........................................................................................................................ 24 Appendix A – Figures ....................................................................................................... 26 Appendix B – Cost Analyses ............................................................................................ 28 Table 1a: Cost Analysis for Selective Catalytic Reduction (SCR) .................................. 28 Table 1b: Cost Analysis for SCR ..................................................................................... 29 Table 1c: Cost Analysis for SCR ..................................................................................... 30 Table 1d: Cost Analysis for SCR ..................................................................................... 31 Table 2: Cost Analysis for Staged Air Combustion......................................................... 32


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Table 3: Cost Analysis for Selective Non-Catalytic Reduction (SNCR) with Staged Air........................................................................................................................................... 32 References ......................................................................................................................... 33


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Acknowledgement

AQMD appreciates the assistance of Mr. Alvaro Linero, Program Manager/New Source Review, of the Florida Department of Environmental Protection during the preparation of this assessment. His support and input proved very valuable in putting this document together.


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Purpose of Draft Update

The Draft Best Available Retrofit Control Technology (BARCT) Assessment document was originally prepared in September 2006 to determine what NOx emission levels should potentially be considered as BARCT in relation to NOx emissions from Cement Manufacturing facilities, particularly the TXI Riverside Cement facility located in Riverside, California. This draft document is subsequently revised and updated on August 8, 2008 in order to:

• update the operational status of the Solnhofer Portland Zementwerke SCR project in the section under “Controls”, “Destroying NOx”, “Selective Catalytic Reduction (SCR)”, and

• incorporate the technology transfer case studies and summary (April 26, 2007 addendum to draft BARCT Assessment document dated September 19, 2006) in the section under “Analysis”, “Technology Transfer”.


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Executive Summary The white cement kilns located at TXI Riverside Cement (TXI) are the subject of this Best Available Retrofit Control Technology (BARCT) assessment. TXI currently utilizes process and combustion control approaches in order to ensure proper kiln operation. These approaches provide a high quality product and result in some nominal reduction of emissions of oxides of nitrogen (NOx). This BARCT assessment was completed in order to determine whether the process and combustion control approaches utilized by TXI constitute BARCT or if more stringent emission limits should apply. The NOx control strategies evaluated for applicability to the white cement manufacturing process were:

• Staged air combustion,

• Selective Catalytic Reduction (SCR), and

• Selective Non-Catalytic Reduction (SNCR)

NOx controls considered appropriate fall into two categories: reducing NOx formation and NOx destruction. SNCR is being utilized on similar kilns in Europe and shows very good control potential. Staged air combustion is being utilized on many kilns and has proven itself to be an excellent primary method to reduce the formation of NOx. It was determined that although SNCR and staged air combustion are significant control approaches for NOx, they cannot be recommended as BARCT for TXI’s white cement kilns at this time. It was concluded that they are very likely cost effective control techniques; however, a manufacturer’s emission reduction guarantee could not be obtained. SCR was found to meet all of the Achieved in Practice (AIP) criteria for BARCT and is being recommended for controlling NOx emissions at TXI.

Introduction

Regulation XX – Regional Clean Air Incentives Market (RECLAIM) program was adopted in 1993. The purpose of RECLAIM is to reduce NOx and SOx emissions through a market-based program. It is designed to provide facilities with flexibility to seek the most cost-effective solutions to reduce their emissions. The program replaced a series of existing command-and-control rules and control measures specified in the 1991 AQMP. NOx and/or SOx allocations were issued to RECLAIM facilities based on their historical activity levels and applicable emission limits. In general, annual allocations are determined pursuant to Rule 2002(f), unless it is determined that additional reductions are necessary to meet air quality standards as part of the AQMP process. Facilities have the option of complying with their allocation allowance by either reducing their emissions or purchasing RECLAIM Trading Credits (RTCs) from other facilities.


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For compliance years between 1994 and 2000, allocations were determined by a straight line rate of reduction between the starting allocation and the year 2000 allocation. For the years 2001 and 2002, the allocations were determined by a straight line rate of reduction between the year 2000 and year 2003 allocations. NOx allocations for 2004, 2005, and 2006 are equal to the facility’s 2003 allocation. For compliance years 2007 and thereafter, the allocations are determined according to the factors in Rule 2002(f)(1)(A) (“the shave”). A facility may request exemption from the shave by showing that they meet the criteria in Rule 2002(i)(2). If granted, the exemption will not apply to any reductions resulting from future periodic BARCT review. Therefore, before TXI can expect to obtain the approval of the Executive Officer they must demonstrate that they are at or below BARCT. During discussions with TXI regarding how they may qualify for an exemption from the shave, staff became aware that TXI was complying with a NOx emission limit of 2.73 lb NOx per ton clinker. This factor was established for gray portland cement kilns only. The factor was removed from the facility permit of TXI and they are now pursuing an appeal of this action in the Hearing Board. Although a careful BARCT review was done for gray portland cement kilns no such review was ever conducted for white cement kilns. This document addresses the cement kilns operated by TXI since they are the only white cement kilns operated within the South Coast Air Quality Management District (AQMD). A general overview of the relevant history of cement and the cement manufacturing process is presented. Applicable NOx control technologies for cement kilns, and their candidacy for BARCT will be discussed. In order for a control technology to be considered BARCT, it must meet minor source Best Available Control Technology1 (MSBACT) criteria. MSBACT is the most stringent emission limit or control technology that is:

• included in a state implementation plan (SIP), or

• achieved in practice (AIP), or

• is technologically feasible and cost effective. This review will look at all applicable and available controls to determine if cost effective control can be applied to the white portland cement kilns operated at TXI Crestmore operations.

History of Cement

Portland cement (cement) is the key ingredient of concrete, which is the most widely used building material on earth. Cement is used as the binding agent in concrete. The Assyrians and Babylonians used clay as a bonding substance or “cement.” The Egyptians used lime and gypsum cement. The first modern hydraulic cement (cures under water)


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was made in England in the mid 18th century and consisted of a mixture of pebbles, powdered brick, and cement. Portland cement was invented in the early 19th century by an English brick mason, Joseph Aspdin, and has remained the dominant cement used in concrete production. Aspdin named it “portland” cement because its color resembled the stone quarried on the Isle of Portland off the British Coast. The first true artificial cement was made by burning ground limestone and clay together. The burning process changed the chemical properties of the materials thereby creating a stronger cement than had been produced previously with crushed limestone.2 The first portland cement plants outside of England were constructed in Belgium and Germany around 1855. Portland cement imports into the United States began in the late 1860s. The first portland cement plant in the United States began operation in 1871.3 Worldwide, the United States ranks third in cement production behind China and India. There are several varieties of portland cement. All portland cements meet the American Society for Testing and Materials (ASTM) standard C-150. Straight portland cement is defined as “a finely ground mixture of portland cement clinker and a small quantity of calcium sulfate hemihydrate, usually in the form of gypsum”3. The different varieties of straight portland cement are designated by the ASTM standard C-150 as follows:

Type I: General use portland cement; sometimes known as ordinary portland cement.

Type II: General use portland cement demonstrating moderate sulfate resistance

and moderate heat of hydration.

Type III: High early strength portland cement.

Type IV: Portland cement having a low heat of hydration.

Type V: Portland cement having high sulfate resistance. For Types I, II, and III, the addition of the suffix A refers to the inclusion of an air-entraining agent. Air entrained concrete is produced through the use of air entraining portland cement, or by introducing air entraining admixtures under careful engineering supervision as the concrete is mixed on the job. The amount of entrained air is usually between 5 percent and 8 percent of the volume of the concrete. The use of air entraining agents results in concrete that is highly resistant to severe frost action and cycles of wetting and drying or freezing and thawing and has a high degree of workability and durability.4 White portland cement has essentially the same properties as gray cement, except for its color. An important quality control issue in the industry, the color of white cement depends on raw materials and the manufacturing process. Metal oxides, primarily iron and manganese, negatively influence the whiteness and undertone of the material. White cement is manufactured to conform to ASTM standard C-150. Types I and III are the most common, but Types II and V are also produced to a lesser extent. 4


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Typical uses of cement include pavement, sidewalks, reinforced concrete buildings, bridges, railway structures, tanks, reservoirs, culverts, water pipe and masonry units. White cement applications include architectural, decorative and structural concrete, tile grout, swimming pools and spas, concrete brick, concrete median traffic barriers, and architectural concrete masonry units. Cement is currently manufactured at 118 facilities in the United States and 16 facilities in Canada, for a total of 134 facilities in North America excluding Mexico. In 2005, about 93 millions tons of portland cement were produced in the United States. An additional 29 million tons of cement and clinker were also imported, primarily from Canada, China, Thailand, and Venezuela5. Within the AQMD, there is one gray cement manufacturing facility in Colton, CA (CPC) and one white cement manufacturing facility in Riverside, CA (TXI). White portland cement facilities account for approximately 3% of total portland cement facilities in North America. There are three white cement facilities in the United States. Besides the facility located in Riverside CA, the two others are located in Waco, Texas, and York, Pennsylvania. There is one white cement plant in Canada. The white cement plants in Texas and Pennsylvania do not contribute very much, if at all, to the market in California and the Canadian plant does not export to California. Therefore, in California the white cement market is supplied by the Riverside facility and is augmented with imports from Korea and Thailand6.

Cement Manufacturing Process

The manufacture of portland cement consists of the following main steps: blending of raw material in either a slurry or dry solids, burning to clinker followed by fine grinding of the clinker with gypsum and other minor additives to make the finished cement product. Raw materials are quarried, crushed, and blended into a kiln feed called raw mix. The process of converting the raw mix into clinker is called pyroprocessing. Traditionally cement clinker was produced in long refractory brick-lined, cylindrical, rotary kilns. Typical kilns are 10 to 25 feet in diameter and 150 to 750 feet in length. The kiln rotates at a typical speed of 1 to 3 revolutions per minute about the longitudinal axis, which is slightly inclined to the horizontal. The raw mix is fed continuously to the kiln at the high “cool” end and progresses down the kiln, and is gradually heated and transformed into semifused nodules as the mix reaches its clinkering temperature. The clinker exits from the lower end of the kiln and falls into a clinker cooler where the clinker is quenched and the temperature is reduced to a safe handling level using water sprays and air injection prior to grinding into cement.7 In the case of white cement, the clinker is sprayed with water prior to exiting the kiln. The water sprays serve as a quench necessary for color preservation. The manufacture of cement by the wet or dry process requires large amounts of energy in the form of fuel necessary to raise the mix to its clinkering temperature. Electrical energy


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is also required to drive size reduction equipment necessary to reduce the feed to an optimal size, to rotate the kiln, and to drive equipment used to grind clinker. On average, approximately 5 million Btu are required to make a single ton of clinker.3 As was mentioned under the history, white cement must be made with a low iron content in order to preserve its value as a cosmetic cement. The lower iron content in the raw mix does not promote the formation of tetracalcium aluminoferrite. This is significant because tetracalcium aluminoferrite functions as a clinkering flux allowing the formation of clinker at a lower temperature. In the absence of iron, or in low iron concentrations, this compound is not formed and hence, higher temperatures and longer residence time is necessary for white cement clinker formation. Therefore, the energy demand for the manufacture of white cement is higher than that required in the manufacture of gray portland cement. The energy requirement for the manufacture of white cement is estimated to be twice that for gray cement when compared on a dry process basis (or approximately 10 million BTU/ton of clinker).6

Kiln Types and Operation

There are four main types of kiln configurations used in the manufacture of portland cement: long wet kilns, long dry kilns, dry kilns with preheaters, and dry kilns with preheaters/precalciners.

Long Wet Kilns

Wet process kilns are the oldest type of rotary kilns used to produce cement clinker. Process chemistry is easier to control using a wet process. The raw mix is blended to a very uniform consistency and the various components are distributed evenly throughout the mix. The wet process is advantageous for moist raw materials. The raw mix is ground in a slurry which is fed into the high end of the kiln (see Figure 1). The slurry is heated and dried simultaneously. Since large quantities of water must be evaporated in addition to the other heat requirements, the energy required for wet process kilns is higher than for dry process kilns. This energy requirement is approximately 6 million Btu per ton of clinker4. The Lehigh white cement plants in Waco Texas and York Pennsylvania are both wet process types.

Dry Kilns

In dry kilns, the raw mix is dry. The operation of dry kilns is similar to that of wet kilns except for the need to evaporate water. Energy demands for dry process kilns are significantly lower than for wet process. The TXI plant in Riverside California is a dry process type without preheaters or a precalciner.


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Dry Kilns with Preheaters

Dry process kilns have improved thermal efficiency and productive capacity through the addition of one or more cyclone-type preheater vessels. The vessels are arranged in series vertically, and are supported by a preheater tower. Hot exhaust gases from the rotary kiln pass countercurrently through the downward-moving raw mix in the preheater vessels. The heat transfer rate is significantly increased compared to the traditional dry process and the process time is reduced by the contact of the solid particles with the hot gases. The improved heat transfer allows the length of the rotary kiln to be reduced.

Dry Kilns with Precalciners

Thermal efficiency and productivity can also be improved by diverting some fuel to a calciner vessel at the base of the preheater tower. This system is called the preheater/precalciner process (Figure 2). A second burner carries out calcination in a separate vessel called the calciner. The calciner utilizes preheated combustion air drawn from the clinker cooler or kiln exit gases and is equipped with a burner that typically burns about 60% of the total fuel. The raw material is calcined about 95% and the gases continue through the cyclone preheater stages. The precalciner system permits the use of even shorter kilns than those described earlier since clinkering is the only process carried out in the kiln. Precalciner technology is the most modern and almost all new cement plants are based on this design.

Fuels

The most common fuels used in cement kilns are coal, natural gas, and residual fuel oil. The amount of nitrogen and the form in which it is found varies depending on the type of fuel. Refined oils generally contain less fuel bound nitrogen. Residual oils can contain up to 0.6% fuel bound nitrogen. Natural gas contains some nitrogen, but it is in the form of nitrogen gas, which does not contribute to fuel NOx.8

Emissions

Particulate matter (PM and PM10), nitrogen oxides (NOx), sulfur dioxide (SO2), and carbon monoxide (CO) are the primary air contaminants typically emitted from the cement manufacturing process. The use of alternative fuels, such as hazardous waste, may also result in emissions of toxic organic chemicals like dioxins, furans and heavy metals such as lead and mercury. The cement industry is considered to be a significant source of NOx emissions. The conditions favorable to the formation of NOx are reached routinely due to the flame temperature. Various mechanisms contribute to NOx formation; the mechanisms are thermal, fuel, feed, and prompt NOx. Thermal and fuel NOx are the primary formation mechanisms.


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Thermal NOx

Thermal NOx is the dominant type of NOx formed and accounts for approximately 70% of total NOx emissions from cement manufacturing. Thermal NOx is the oxidation of molecular nitrogen present in the combustion air. Thermal NOx is formed chiefly by two reactions, both of which are dependent on the dissociation of atmospheric O2 and N2:

O + N2 → NO + N O2 + N → NO + O

The formation of thermal NOx increases rapidly with even small increases in temperature when temperature is in the range of 2500 – 3400 °F. The sintering zone of kilns has temperatures conducive to the formation of thermal NOx. Small shifts in the oxygen content of combustion gases in the kiln’s sintering zone can have a pronounced effect on the amount of thermal NOx formed.

Fuel NOx

Fuel NOx is the oxidation of nitrogen compounds present in the fuel9. Fuel NOx refers to NOx formed by the combustion of nitrogen compounds in the fuel. Most fuels (except natural gas) contain nitrogen compounds in some amount. The oxidation of nitrogen in fuels occurs throughout the entire temperature range of combustion in the kiln. Based on its nitrogen content, coal has the highest potential to generate fuel NOx and natural gas has the least.

Feed NOx

Feed NOx develops from the oxidation of nitrogen compounds in the raw materials. Feed NOx tends to form at relatively low temperatures (626 – 1472°F), especially when the rate of heating is slow. Feed NOx contributions tend to be greater in wet and long dry kilns than in preheater and precalciner kilns. 3

Prompt NOx

Prompt NOx is formed by fuel-derived radicals, such as CH and CH2, reacting with atmospheric nitrogen. Prompt NOx refers to the NO formed in fuel-rich flames that is in excess of what would be expected to form by thermal NOx reactions. It appears to be formed by the reaction of CH2

-2 and other fuel-derived radicals with atmospheric nitrogen to form cyanide radicals and nitrogen radicals. The cyanide and nitrogen radicals oxidize to NO.


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Controls

NOx controls for the cement industry may be categorized as follows:

1. Process and combustion controls where the emphasis is on reducing NOx formation, and

2. Post-combustion controls which destroy the NOx formed in the combustion process.

Reducing NOx Formation

Process and Combustion Modification

Process and combustion modifications are usually the first steps taken when attempting to reduce NOx emissions from cement kilns. Process modifications that result in an increase in the thermal efficiency of the kiln are important steps toward achieving NOx emission reductions from cement kilns. Utilizing an efficient chain system (improving the heat transfer to the raw mix from chains hanging from the interior kiln wall), reformulation of raw mix material, and increasing heat recovery from the clinker cooler are all important steps in improving the thermal efficiency of the kiln and minimizing NOx emissions. Combustion modifications include fuel selection, controlling excess air, modifying burners, and varying air-to-fuel ratios. Although process and combustion control approaches reduce NOx emissions, these approaches do not result in significant reductions and should be used to augment other control strategies. These approaches are considered necessary for proper kiln operation and are thus not considered to be bona fide stand alone NOx control techniques.

Staged Combustion Air, Indirect Firing with Low-NOx Burners

Nitric oxide is formed at high temperatures in the presence of nitrogen and oxygen. As indicated above, in the cement making process, the formation of clinker requires temperatures in excess of 2700°F (gas phase temperature in excess of 3000°F). Due to this high temperature and the availability of nitrogen (nitrogen present in the combustion air and the fuel) and oxygen, NOx is formed. Therefore, methods to reduce NOx emissions should be based on reducing the conditions that favor the formation of NOx. This may be achieved by reducing the oxygen concentration in the high temperature combustion zone, reducing combustion temperature, and reducing the gas residence time in the high temperature zone. The best example of an effective technique for reducing the formation of NOx is the staging of combustion air while burning coal in a cement kiln. With this method, the combustion process occurs in at least two distinct zones. In the first zone, primary combustion takes place in a fuel-rich environment followed by final combustion in the


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presence of secondary air or fuel-lean zone. Most rotary dry kilns are fired directly. In a direct-fired system, air is used to transfer the coal from the coal mill to the burner. Since this air is needed to convey the coal, no changes to reduce the primary air can be made. In direct-fired kilns, the primary air is about 24% to 30% of the total amount required. By converting the kiln from a direct-fired to an indirect-fired system, the amount of primary combustion air can be reduced to less than 10%. The conversion involves the separation of the conveying air from the pulverized coal by sending the conveying air through a baghouse. The pulverized coal collected in the baghouse hopper can then be conveyed to the burner with much less primary air. This reduction in the amount of primary air creates a fuel-rich zone. In this fuel-rich zone, high temperatures necessary for completion of the clinkering reaction are created while the reduction in the primary air results in the reduction of peak flame temperature. In this stage, the reduction in peak flame temperature and the reduction in oxygen results in conditions which minimize the formation of NOx. In the second stage, the secondary air from the clinker cooler is added. Due to the incomplete combustion from the first stage, the combustion of the fuel is completed but at a lower temperature which minimizes the formation of NOx. In this zone, the decrease in temperature is more important than the increase in oxygen in reducing the formation of NOx. The conversion to an indirect-fired system results in NOx emission reductions. It also results in an increased in energy efficiency of the kiln due to the increase in the amount of clinker cooler air used as secondary air. An increase in efficiency of up to 12% is possible due to this conversion. The conversion of a kiln to an indirect-fired system will allow for the use of a low-NOx burner which requires less than 10% primary air. Low-NOx burners are designed to slow the conversion of nitrogen to NOx by delaying the mix of fuel and air in the burner zone. The conversion to an indirect-fired system coupled with a low-NOx burner has been demonstrated in practice to reduce NOx emissions in the range of 30-50%. This conversion does not apply to the kilns at TXI, which currently utilize a low-NOx Pillard burner arrangement designed for fuel oil combustion. There are new developments that are now available to enhance the staging of combustion. This is the injection of high pressure air into the hot process gas to achieve or enhance both the staging of combustion by managing the availability of oxygen in various zones of the kiln, and also by reducing the amount of excess oxygen. The reduction of excess oxygen required is achieved by effectively mixing the cross-section of the gas in the kiln. This method of mixing limits the available oxygen in the primary combustion zone. This is the result of reducing the excess air required and providing the excess air after the primary combustion zone. Staged air combustion alone has been shown to reduce NOx emissions by as much as 50%. Although the hot zone of white cement kilns can be maintained under slightly substoichiometric conditions (which also leads to reduced NOx formation as compared to gray cement kilns), the product quality can be adversely affected if the reducing conditions are too severe. This fact limits the performance of staged air combustion on white cement kilns.10 At the present, staged air combustion does not appear to be a good candidate for NOx control for white cement kilns.


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Secondary Combustion of Fuel

In the cement manufacturing process, heat is necessary for the formation of clinker, the calcining of the material, and the pre-heating of the raw material. In dry kilns, the heat required to achieve all of the above functions is supplied by the burner at the hot end of the kiln. In this zone, very high temperatures (solids temperature in excess of 2700°F) are needed to complete the reaction to form the clinker. However, since the calcining of the material, which occurs prior to the clinker formation, and the heating of the feed material, which takes place at the high end of the kiln, require much less intense heat, a portion of the fuel may be introduced at the mid-section of the kiln. Fuel in the mid-section of the kiln is added in the zone where the temperature is between 1700 and 1900°F in order to provide the heat required to complete the calcining and preheating of the feed material. Due to the rotation of the kiln, it is possible that fuel can be added only once during a revolution from the top of the kiln. In order to maintain a heat input, solid slow burning fuels (such as containerized liquid or solid waste) are the most amenable to this type of modification. Secondary firing may also produce additional fuel NOx depending on the nitrogen content of the fuel. Examples of solid waste include whole or shredded tires, shredded paper and pulp, spent catalysts, sawdust, scrap wood, rubber residues, shredded packing containers, bone meal, scrap fabrics, dried sewage sludge, oil-contaminated soils, and scrap plastics. Examples of liquid waste fuels include a wide range of spent lubricants and solvents, substandard petroleum refinery products, tars, paints and inks, and miscellaneous chemicals, slurries, and sludges. 3 Tires are a typical choice of waste fuel for secondary combustion. The incorporation of tires as secondary combustion fuel can achieve a 25% reduction in NOx emissions. This approach is acceptable for gray cement since the iron present in the tread is a desirable component and there is no danger of discoloring the cement. However, this is not an option for the manufacture of white cement since the iron content of the raw mix has to be kept to a minimum to avoid discoloration of the product. Other substances present in the waste fuel may contribute to discoloration as well.

Destroying NOx

Wet Scrubbing

Use of wet scrubbing requires the treatment of the flue gases with sprays, chemical combatants and filtration systems. This technology has been used successfully in a number of applications and emission reductions of over 90% have been reported. Wet scrubbing requires a significant amount of chemicals and results in a significant wastewater stream. Large amounts of neutralized salts are created as a result of this process and disposal may present a problem. This control technique has not been tested on a cement kiln. Due to the extremely high exhaust gas volumes that need to be treated,


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the significant solid waste impacts, and the interference of CO2 with the NOx-controlling chemicals, this technology is not feasible for long dry white portland cement kilns.

Selective Non-Catalytic Reduction (SNCR)

SNCR utilizes a reducing agent injection (usually urea or ammonia) without the need for a catalyst. NOx emissions from the combustion process can be reduced by injecting selective reducing agents. The ammonia or urea must be injected into the exhaust gases within a temperature window of 1700 to 2000°F. In this temperature range, the reducing agent reacts with NOx forming nitrogen and water. This temperature range limitation is very critical. At temperatures above 2000°F, NOx emissions actually increase rather than decrease and at temperatures below 1700°F, due to the incomplete reaction, ammonia slippage will increase. The injection of a reducing agent in this temperature window has an exceptional potential to reduce NOx emissions by 50% or more. In a conventional long kiln, the appropriate temperature window is near the middle of the kiln. Because of the rotating nature of a long kiln, continuous injection of the reducing agent had been considered infeasible. However, recent advances show promise for the use of SNCR on long wet or dry kilns. A cement plant in Lumbres, France utilizes an innovative SNCR system which is mounted directly on the kiln. This is a long wet kiln and the location of the injector nozzles allows the urea to be injected into the appropriate temperature window. The SNCR system reduced NOx emissions by over 30%. The system has been in operation for about one year and appears to be a promising technology. SNCR destroys NOx by a two-step process as follows: 1. Ammonia reacts with available hydroxyl radicals to form amine radicals and

water according to the following equation: NH3 + OH* → NH2* + H2O 2. Amine radicals combine with nitrogen oxides to form nitrogen and water. NH2* + NO → N2 + H2O 3. The two steps are typically expressed as a single “global reaction”. 4NO + 4NH3 + O2 → 4N2 + 6H2O In preheater/precalciner type cement kilns, the temperatures at the cooler end of the rotary kiln, in the riser duct, and in the lower section of the cyclone preheater tower are likely to be in the temperature window appropriate for SNCR. SNCR is presently being used in 18 preheater or precalciner cement kilns in Europe.11


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Urea Injection (Dry Product)

The introduction of urea at the high end of the kiln in the form of powder or pellets has been considered. While it would be convenient to add the material along with the raw mix, the solid urea is expended before it can reach the optimum point of NOx concentration in the combustion zone, and no appreciable benefit is achieved. This control technology might be feasible in the future.

Selective Catalytic Reduction (SCR)

SCR is very similar to SNCR except that a catalyst is utilized in addition to a reducing agent. The use of a catalyst allows the NOx reduction reactions to be initiated at significantly lower temperatures compared to SNCR. Titanium dioxide and vanadium pentoxide mixtures are the most commonly used catalysts. Ammonia is injected which reacts with NOx. The NOx is decomposed to nitrogen and water according to the following reactions12: 1. 4NO + 4NH3 + O2 → 4N2 + 6H2O 2. 6NO2 + 8NH3 → 7N2 + 12H2O 3. 6NO + 4NH3 → 5N2 + 6H2O 4. NO + NO2 + 2NH3 → 2N2 + 3H2O Traditionally, the optimum temperature for the operation of SCR has been 600 to 900°F; however, new catalysts are available that function well at temperatures as low as 300°F. NOx reduction efficiencies of 90% and higher have been achieved in practice. The NOx concentration in exhaust streams can be reduced to 2 ppmv with the use of SCR, even with low inlet concentrations in the range of 20-30 ppmv NOx. Conventional SCR is subject to poisoning in corrosive environments such as cement kiln exhausts. Particulate emissions, also present in flue gases, may contribute to a greatly shortened catalyst life. Therefore, the SCR unit should either be placed downstream of the dust collector or an integrated dust removal system should be utilized to remove the particulate matter from the catalyst bed. If placed after the dust collector, the flue gases may need to be reheated for optimal SCR performance unless a low temperature catalyst is used. Solnhofer Portland Zementwerke The Solnhofer Portland Zementwerke (SPZ) facility in Germany began operating with SCR in 2001. The catalyst was specifically designed for the cement industry and manufactured by KWH Catalysts, who guaranteed a catalyst lifetime of 2 years, with an expected lifetime of 3-4 years. In 2006, the original catalyst was replaced after over 40,000 hours of operation. Examination of the removed catalyst showed that there was no evidence of catalyst poisoning or deactivation. The problem of heavy fouling from


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the heavy dust loading was managed with an integrated cleaning system. Replacement of the original catalyst, which was a honeycomb type, with plate-type catalyst was expected to reduce plugging problems and allow the operator to scale back on use of the integrated cleaning system. However, activity of the plate-type catalyst declined more rapidly than expected; hence, SPZ switched to SNCR in order to meet their NOx emission limit. SPZ used the opportunity to conduct a comparison between SCR and SNCR before investing in a new set of catalysts. Although SPZ can meet their permit limit solely through the use of SNCR, the consumption of ammonia with SNCR is significantly higher than compared to SCR. SPZ personnel are confident of returning to SCR once management gathers sufficient experience and data for a sound economic decision. Prior to installation of SCR, SPZ was achieving NOx emissions of 4.6 to 7.4 lbs/ton (5.1 to 8.1 lbs/metric tonne) of clinker. With SCR, emissions were reduced to approximately 1.8 to 2.5 lbs/ton of clinker. It has been indicated that the SCR system is capable of achieving a lower NOx emission rate using all of their catalyst beds. Since SPZ’s operating permit only requires compliance with a NOx emission limit of 2.3 lbs/ton (500 mg/Nm3) of clinker, there is no incentive for further reductions.13

Technology Evaluation

TXI Riverside Cement, has made commendable reductions through combustion and process modifications. These modifications have resulted in a more controlled and optimized process, improved fuel efficiency, and have resulted in NOx emissions that are comparable to the newest cement plants in Texas and Florida. These plants utilize preheaters and precalciners and are required to meet emission limits as low as 1.95 lbs of NOx per ton of clinker. Currently, the TXI kilns each emit below 1.5 lbs of NOx per ton of clinker. Utilization of SCR is a very effective method of reducing NOx emissions. NOx emissions will be reduced by 90%, resulting in concentrations below 10 ppm in the exhaust stream. The application of wet scrubbing requires a large chemical plant to treat such a high flue gas volume and generates large amounts of salts. Therefore, the use of wet scrubbing in this application is not practical. Although staged air combustion (mid-kiln) has been used to achieve NOx reductions of as much as 50%, the vendor of this technology cannot guarantee emission reductions in TXI’s case. In addition, product quality from white cement kilns can be adversely affected by the hot zone environment created by this process. SNCR technology appears to be very promising for this application. There are currently two providers of mid-kiln SNCR technology, but only one known installation. Advancement in this technology might make this application more attractive in the future. Note that although the NOx concentration is measured using a CEMS, the actual


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emission rate is estimated based on the fan curve of the exhaust blower. Due to this method of estimation, the emission rate may not be properly estimated.

Cost Effectiveness

Capital and operating costs were considered over a 10-year life span and a dollar value was assigned, using the AQMD’s Pre-Tax, Discounted Cash-Flow method of evaluation. This 10-year cost figure was then divided by the total emissions expected to be controlled over that period in order to arrive at a present value cost in dollar per ton. The capital cost of SCR is estimated to be $1,609,851. The existing open-top baghouses would have to be replaced in order to utilize SCR, so the cost of replacing the baghouses is included in the total capital cost. Based on estimated control efficiency of 90%, the emissions reduction would be 72 tons per year. Based on these figures, the cost effectiveness would be $11,338 per ton (see Cost Analysis in Appendix B) which is below the MSBACT maximum cost effectiveness value of $21,318 (adjusted to 2005 dollars using the Marshall and Swift Equipment Cost Index). A cost effectiveness of $10,615 is estimated if the cost of replacing the baghouses is excluded from the evaluation. The baghouses were installed over 40 years ago and have long exceeded their economic life. The cost of replacing them can be considered to be an expected capital cost. The cost effectiveness was also evaluated at conservative control efficiency of 50%. The resulting cost effectiveness was $20,431 per ton including the cost of replacing the baghouses. The cost effectiveness, excluding the cost of the baghouses, was $19,129 per ton. Both of these cost effectiveness values at 50% control efficiency are below the MSBACT maximum cost effectiveness limit of $21, 318 per ton. According to a study14 performed for The Lake Michigan Air Directors Consortium, the cost effectiveness estimate for SCR for long dry kilns ranged from $586 to $1902 per ton of NOx reduced. A European study15 in 2001 concluded that the cost effectiveness of SCR on kilns with preheaters was about 2.76 Euros per ton of clinker, or $2,273 per ton of NOx removed (adjusted to 2005 dollars) if applied to TXI’s kilns. The studies were based on kilns with much higher levels of uncontrolled emissions, thereby reducing the total cost per ton of pollutant reduced. An increase in the selling price of cement is expected if SCR is implemented. The incremental increase, assuming that the cost of replacing the baghouses can be ignored, is $8.40 per ton of cement. The average selling price of white cement in the United States in 2004 was $164 per ton. The selling price, adjusted to fourth quarter 2005 dollars using the Marshall & Swift Equipment Cost Index, is $167.50. Therefore, a price increase of 5.0% would result from the installation of SCR. Although the estimated cost effectiveness of staged air combustion and staged air with SNCR is below the MSBACT maximum cost effectiveness value, the emission


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reductions are based on expected control efficiency and are not guaranteed by the vendor. Until an emission reduction guarantee can be provided, these control technologies will not be considered BARCT candidates.

Analysis

As stated in the Introduction, MSBACT is the most stringent emission limit or control technology that is:

• included in a SIP, or

• achieved in practice, or

• is technologically feasible and cost effective. Technology transfer is considered across source categories. There are two types of potentially transferable control technologies: 1) exhaust stream controls, and 2) process controls and modifications. For the first type, technology transfer must be considered between source categories that produce similar exhaust streams. For the second type, process similarity governs the technology.1

State Implementation Plans

The State of Florida has the most stringent emission limit adopted by any state as a rule, regulation or permit and approved by USEPA. Florida has imposed an emission limit of 1.95 pounds of NOx per ton of clinker on several cement facilities. The emission limit can be found in USEPA’s RACT/BACT/LAER Clearinghouse. Although this limit applies to gray cement kilns, TXI can be expected to meet the limit as well since the reduced oxygen in the hot zone of the kiln leads to less NOx formation than in gray cement kilns. TXI is currently operating at levels below this emission limit; therefore, 1.95 pounds of NOx per ton of clinker cannot be considered MSBACT or BARCT.

Achieved in Practice

MSBACT may also be based on the most stringent control technology or emission limit that has been achieved in practice (AIP) for a category or class of source. AIP control technology may be in operation in the United States or any other part of the world. A control technology or emission limit may be considered as AIP if it meets all or the following criteria:

• Commercial Availability: At least one vendor must offer this equipment for regular or full-scale operation in the United States. A performance warranty or

1 AQMD BACT Guidelines, July 14, 2006.


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guarantee must be available with the purchase of the control technology, as well as parts and service.

• Reliability: The control technology must have been installed and operated reliably for at least twelve months on a comparable commercial operation. If the operator did not require the basic equipment to operate continuously, such as only eight hours per day and 5 days per week, then the control technology must have operated whenever the basic equipment was in operation during the twelve months.

• Effectiveness: The control technology must be verified to perform effectively over the range of operation expected for that type of equipment. If the control technology will be allowed to operate at lesser effectiveness during certain modes of operation, then those modes must be identified. The verification shall be based on a performance test or tests, when possible, or other performance data.

• Cost Effectiveness: The control technology or emission rate must be cost effective for a substantial number of sources within the class or category. Cost effectiveness criteria are described in detail in a later section. Cost criteria are not applicable to an individual permit but rather to a class or category of source.

Technological Feasibility and Cost Effectiveness

SCR is technologically feasible for exhaust streams from cement kilns. Its cost effectiveness has been evaluated and found to meet the MSBACT maximum cost effectiveness criteria. Although TXI operates below the most stringent SIP emission limits, additional reductions are possible through the implementation of SCR. Additionally, SCR would require the replacement of TXI’s obsolete open-top baghouses. The current configuration does not allow for actual flow measurements. The new configuration would allow for accurate flow measurements downstream of the baghouse. The resulting flow measurements would ensure that the reported emission data is correct. TXI’s current emission levels cannot be considered BARCT. SCR would achieve considerable additional reductions and has been shown to meet all of the MSBACT criteria; therefore, SCR is BARCT for this source.

Technology Transfer

SCR has been shown effective on exhaust streams similar to that of cement kilns.

• Case Studies

CRI Catalyst’s low temperature SCR technology, referred to as the Shell DeNOx System (SDS), is able to operate at lower temperatures and lower pressure drop


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than traditional SCR. Consequently, the SCR system can be installed immediately before or in the stack, avoiding any modification to combustion or heat recovery equipment. This makes the Shell SDS very suitable for retrofit SCR applications.2 In the case of TXI, the SDS would be installed downstream of a new baghouse. Hence, the exhaust stream would be similar to those of other combustion equipment which utilize SDS technology, such as gas turbines, ethylene crackers furnaces, boilers, waste incineration plants, and process heaters.

Gas Turbine Installations The Shell SDS technology has been retrofitted on 15 gas turbines, at facilities in California, the Gulf Coast, and the Netherlands. Stack gas temperature for these installations ranges from 325 – 400 °F. NOx reduction ranges from 89% - 94%. In 1997, three turbines at a Bay Area facility were retrofitted with Shell SDS. The SCR was designed for a flue gas flow rate of 1,030,000 lbs/hr and a minimum operating temperature of 375 °F. The fuel to the turbines is natural gas. Design performance was 9 ppmvd maximum NOx outlet from a maximum of 135 ppmvd NOx inlet, or a 93% NOx reduction. The units operate within the NOx emission limits and NH3 slip requirements (10 ppmvd).

Parameter Design Start Up 3/1997 12/2001

Months since start up -- 0 57

SCR Operating Temp 375 °F 377 °F 411 °F

Flue Gas Flow, lbs/hr 1,030,000 max 920,000 920,000

NOx inlet, ppmvd @ 3% O2

135 121 110

NOx outlet, ppmvd @ 3% O2

9 5 4

NOx Reduction 93.3% 95.9% 96.3%

NH3 Slip @ 3% O2 10 - 5

Ethylene Cracker Furnaces The Shell SDS technology has been retrofitted on two ethylene cracker furnace facilities: six furnaces in Germany and two furnaces in the Netherlands. The fuel to the furnaces is either fuel gas produced on site or natural gas. Stack gas temperature for these installations ranges from 285 – 420 °F. NOx reduction ranges from 65% - 91%. In 2000, two ethylene cracker furnaces at Shell Nederland Chemie in the Netherlands were retrofitted with SDS technology to bring the site into compliance with lower total NOx emission requirements. The SCR units were designed to treat a flue gas flow of

2 CRI Catalyst, Retrofit Application and Operation of the Shell Low Temperature SCR Technology on Gas Turbines, Ethylene Cracker Furnaces, and Process Heaters, ICAC Forum ’02, February 12-13, 2002.


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approximately 190,000 lbs/hr and achieve 91% minimum NOx reduction (from 102 ppm at 3% O2 to 9.7 ppm) with 5 ppm maximum NH3 slip. At startup, the NOx reduction ranged from 94.6% - 97.5% with NH3 slip of 1-1.5 ppm. The NOx inlet was 75-80 ppm and the outlet was 2-4 ppm. The units continued to operate within the NOx emission limits and NH3 slip requirements.

Parameter Design Start Up 6/2000 1/2001

Months since start up -- 0 6

SCR Operating Temp 410 °F 404 °F 392 °F

NOx inlet, ppmvd @ 3% O2

102 75-80 95

NOx outlet, ppmvd @ 3% O2

9.7 2-4 3.5

NOx Reduction 90.5% 94.6-97.5% 96.2%

NH3 Slip @ 3% O2 6.6 1-1.5 1.5

Refinery Heaters The SDS technology has been retrofitted on five refinery heaters/furnaces. Fuel to the units is primarily refinery fuel which contains varying levels of sulfur. SCR operating temperatures for these units ranges from 350 – 450 °F. Operating parameters for three such systems is shown below:

Location Start-up

Date

Flue Gas Flow, lbs/hr

Temp, °F

Design Max NOx Conc,

Outlet

Design NOx

Reduction

Design NH3 Slip

California 3/1991 60,000 420 9 ppm 87% 10 ppm

California 11/2000 700,000 440 20 ppm 92% 10 ppm

Sweden 10/1998 275,000 350 9 ppm 90% 5 ppm

• Summary

The exhaust stream from TXI’s white cement kilns is approximately 92,000 lbs/hr and has an inlet NOx concentration of about 50-60 ppm, but may range up to 215 ppm. The temperature of the exhaust is about 325 °F downstream of the baghouse. These levels are similar to exhaust streams of many processes which currently utilize CRI’s SDS technology. The SDS technology from CRI is capable of significant NOx reductions when installed in an exhaust stream that is considered clean, or has very low particulate concentration. The technology has been used in exhaust streams with comparable NOx concentrations and achieved reductions in excess of 90%.


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Conclusion

SCR meets all of the criteria for AIP MSBACT. It is commercially available in the United States. It has been installed and has operated reliably for over 4 years on a comparable commercial operation in Germany. The control technology is guaranteed to perform at a minimum 90% control efficiency. The cost effectiveness was evaluated for two basically identical permits, which can be deemed a similar class or category of source. SNCR and staged air combustion are promising candidates for future MSBACT evaluations. However, they cannot be recommended for MSBACT at this time, primarily due to the lack of an emissions reduction guarantee.


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APPENDICES


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Appendix A – Figures

Figure 1: Typical Wet Process Kiln 15


27

Figure 2: Typical Dry Kiln with Preheaters and Precalciner16


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Appendix B – Cost Analyses

Table 1a: Cost Analysis for Selective Catalytic Reduction (SCR)

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Purchased equipment cost = $350,000 per kiln (neglecting cost of replacing baghouses) Direct installation cost = $500,000 per kiln (estimate provided by vendor)17 Indirect installation cost = $500,000 per kiln (estimate provided by vendor) Total capital cost (C) = $1,350,000 per kiln Chemical cost = $240,000 per year Catalyst replacement cost = $200,000 * A/F(4%, 3 years) = $200,000 * (0.3203) = $64,060 (assuming three-year replacement cycle) Total annual cost (A) = $240,000 + $64,060 = $304,060 per kiln Present value (PV)= $1,350,000 +$304,060*(8.111) = $3,816,231 per kiln = $7,632,462 Emissions reduced = 90% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs

= 719 tons Cost of control = $7,632,462 / 719 = $10,615/ton Note: Durr Systems stated that their SCR will achieve 95% NOx reduction; however, 90%, as given by CRI Catalyst, was used as a conservative estimate for both SCR systems. Both Durr Systems and CRI Catalyst indicated that a single SCR unit may be able to control emissions from both kilns; however, this assumption cannot be made at this time since additional data and slipstream testing are required.


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Table 1b: Cost Analysis for SCR

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Purchased equipment cost = $609,851 per kiln (including cost of replacing baghouses) Direct installation cost = $500,000 per kiln Indirect installation cost = $500,000 per kiln Total capital cost (C) = $1,609,851 per kiln Chemical cost = $240,000 per year Catalyst replacement cost = $200,000 * A/F(4%, 3 years) = $200,000 * (0.3203) = $64,060 (assuming three-year replacement cycle) Total annual cost (A) = $240,000 + $64,060 = $304,060 per kiln Present value (PV) = $1,609,851 +$304,060*(8.111) = $4,076,082 per kiln = $8,152,164 Emissions reduced = 90% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs

= 719 tons Cost of control = $8,152,164 / 719 = $11,338/ton


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Table 1c: Cost Analysis for SCR

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Purchased equipment cost = $350,000 per kiln (neglecting cost of replacing baghouses) Direct installation cost = $500,000 per kiln (estimate provided by vendor)18 Indirect installation cost = $500,000 per kiln (estimate provided by vendor) Total capital cost (C) = $1,350,000 per kiln Chemical cost = $240,000 per year Catalyst replacement cost = $200,000 * A/F(4%, 3 years) = $200,000 * (0.3203) = $64,060 (assuming three-year replacement cycle) Total annual cost (A) = $240,000 + $64,060 = $304,060 per kiln Present value (PV)= $1,350,000 +$304,060*(8.111) = $3,816,231 per kiln = $7,632,462 Emissions reduced = 50% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs

= 399 tons Cost of control = $7,632,462 / 399 = $19,129/ton Note: Durr Systems stated that their SCR will achieve 95% NOx reduction; however, 50% reduction is being used in this scenario strictly for cost effectiveness evaluation. Both Durr Systems and CRI Catalyst indicated that a single SCR unit may be able to control emissions from both kilns; however, this assumption cannot be made at this time since additional data and slipstream testing are required.


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Table 1d: Cost Analysis for SCR

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Purchased equipment cost = $609,851 per kiln (including cost of replacing baghouses) Direct installation cost = $500,000 per kiln Indirect installation cost = $500,000 per kiln Total capital cost (C) = $1,609,851 per kiln Chemical cost = $240,000 per year Catalyst replacement cost = $200,000 * A/F(4%, 3 years) = $200,000 * (0.3203) = $64,060 (assuming three-year replacement cycle) Total annual cost (A) = $240,000 + $64,060 = $304,060 per kiln Present value (PV) = $1,609,851 +$304,060*(8.111) = $4,076,082 per kiln = $8,152,164 Emissions reduced = 50% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs



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Table 2: Cost Analysis for Staged Air Combustion

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Capital cost (C) = $300,000 per kiln (Installed cost provided by vendor)19 Total annual cost (A) = $0 Present value (PV) = $300,000 * 2 (for both kilns) = $600,000 Emissions reduced = 30% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs

= 240 tons Cost of control = $600,000 / 240 = $2,505/ton

Table 3: Cost Analysis for Selective Non-Catalytic Reduction (SNCR) with Staged Air

Cost of control = present value/emissions reduced over the equipment life Present value (PV) = C + A*P/F(r, n) Where, Equipment life (n) = 10 years Real interest rate (r) = 4% Capital cost (C) = $300,000 per kiln Chemical cost = $0.50 per year, per ton of clinker produced Total annual cost (A) = $0.50 * 106,469 tons/yr = $53,235 per year (for both kilns) Present value (PV) = $300,000 * 2 +$53,235*(8.111) = $1,031,789 (for both kilns) Emissions reduced = 40% * (1.5 lbs/ton * 106,469 tons/yr * 1 ton/2000 lbs) * 10 yrs



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References

1 SCAQMD Minor Source BACT Guidelines, December 2003. 2 Bellis, Mary, The History of Concrete and Cement. 3 U.S. Geological Survey (USGS), Background Facts and Issues Concerning Cement and Cement Data. 4 Portland Cement Association, Cement and Concrete Basics. 5 USGS, Mineral Commodity Summaries, January 2006. 6 Discussion with TXI representative Gregory Knapp on 2/9/2006. 7 USGS Background Facts and Issues Concerning Cement and Cement Data. 8 Zevenhoven, Ron and Kilpinen, Kia, Control of Pollutants in Flue Gases and Fuel Gases, Laboratory of Energy Engineering and Environmental Protection, 2002. 9 U.S. EPA, Alternative Control Techniques Document – NOx Emissions from Cement Manufacturing, 1994. 10 Email communication with Cadence Combustion Technology representative Eric Hansen, March 3, 2006. 11 Assessment of NOx Emissions Reduction Strategies for Cement Kilns – Ellis County and Across Texas, ERG for TCEQ, 2005. 12 CRI Environmental Catalyst and Systems, A Catalytic System for NOx and Dioxins Removal, Applications, Performance, and Costs, March 2001. 13 German BREF Contribution, German Federal Environmental Agency, June 2006. 14 LADCO, prepared by MACTEC, Midwest RPO Cement BART Engineering Analysis, March 2005. 15 Kossina, Isabella, Reduction of NOx Emissions from Exhaust Gases of Cement Kilns by Selective Catalytic Reduction, Proceedings of NOx Conference, March 2001. 16 U.S. EPA, Draft Technical Support Document for HWC MACT Standards, February 1996. 17 Email communication with CRI Criterion Catalyst Sales Manager Robert Remkes. 18 Email communication with CRI Criterion Catalyst Sales Manager Robert Remkes. 19 Discussion with Cadence Combustion Technology representative Eric Hansen, March 1, 2006.

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