training course for biogas project operation managerscellulose, hemicellulose, pectin, and...

Output Five for Study on Market-based Mechanism for Large and Medium-sized Biogas Projects Operation

Training Course for

Biogas Project Operation Managers

Energy and Environmental Development Research Center

March, 2010

CONTENT

1． BASIC KNOWLEDGE...................................................................................... 1

1.1. DEFINITION AND PROPERTY OF BIOGAS............................................................ 1 1.2. PRINCIPLE OF BIOGAS FERMENTATION ............................................................. 2 1.3. CONDITIONS FOR BIOGAS FERMENTATION........................................................ 3

2． OPERATION OF LARGE- AND MEDIUM-SCALE BIOGAS PROJECTS....... 7

2.1. TECHNOLOGY OF LARGE- AND MEDIUM- SCALE BIOGAS PROJECTS .................. 7 2.2. INTRODUCTION OF INDIVIDUAL UNIT OF BIOGAS PROJECT................................. 8

3． OPERATION MANAGEMENT OF LARGE- AND MEDIUM-SCALE BIOGAS PROJECTS............................................................................................................... 10

3.1. MANAGEMENT REGULATIONS......................................................................... 10 3.2 OPERATION MANAGEMENT OF PROJECT UNITS................................................... 12 3.3 SAFETY MANAGEMENT OF PROJECT UNITS......................................................... 17

4． MAINTENANCE MANAGEMENT OF BIOGAS PROJECT........................... 19

4.1 MAINTENANCE OF FACILITIES ........................................................................... 19 4.2 GENERAL PRINCIPLES OF MAINTENANCE.......................................................... 19 4.3 MAINTENANCE OF ELECTRICAL INSTRUMENTS AND METERS.............................. 20 4.4 MAINTENANCE OF PUMPS ................................................................................ 21 4.5. MAINTENANCE OF WARMING INSTALLATIONS.................................................... 21 4.6 MAINTENANCE OF SOLID-LIQUID SEPARATORS.................................................. 23 4.7 MAINTENANCE OF OPERATIVE UNITS................................................................ 23 4.8 OTHER CONSIDERATIONS ................................................................................ 25

5 SECURITY......................................................................................................... 25

5.1 DANGER SOURCE............................................................................................ 25 5.2 DANGER PREVENTION MEASURES ................................................................... 26

The Training Course for Biogas Project Operation Managers

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1． Basic Knowledge

1.1. Definition and Property of Biogas

1） What is Biogas？

In hot summer or autumn, as can often be observed, small bubbles emerge from the surface of stagnant pools, sewage ditches and manure tanks. If these small bubbles are collected and ignited, they can burn in a blue flame. This flammable gas is called biogas.

In nature, biogas is a gas fuel generated from organic materials, such as animal manure, sewage and green waste, through fermentation by anaerobic micro-organism under favorable conditions of moisture, temperature and absence of oxygen. As a convenient, clean, high-quality and high-grade fuel, biogas can be directly used for cooking, lighting, power-generating, heating, drying and grain-storing.

2） Composition of Biogas

Biogas is a gas mixture mainly composed of methane. The composition of biogas varies depending upon the types and relative contents of different raw materials, as well as upon the different conditions and fermenting phases. Under normal conditions, the main components of biogas are methane(CH4) amounting for 50%～70%, carbon dioxide(CO2) amounting for 30%～40%, and smaller amounts of hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), nitrogen (N2) and other gases.

3） Properties of Biogas

Biogas is colorless, and before the removal of its hydrogen sulfide (H2S), it smells like bad egg. After burning, the bad smell also disappears. As biogas consists mainly of methane, its physical and chemical properties are similar to those of the latter.

Calorific Value： Methane is a high-quality gas fuel with a very high calorific value. In the standard condition, 1m3 pure methane releases 35,822 kJ of heat through complete combustion, with the maximum temperature of 1400 ℃. As the biogas is a mixture with other ingredients, it has a lower calorific value 20,000～29,000 kJ, with the maximum temperature of 1200 ℃.

Specific Gravity： The specific gravity of methane is 0.55 and that of biogas is 0.94. In biogas tanks, the methane is floats in the upper space, while the heavier carbon dioxide stays at the bottom. Since biogas is lighter than air, it disperses quickly in the atmosphere, four times as rapid as the air.

Solubility： The solubility of methane in water is very low: at 20 ℃ under one


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atmospheric pressure, only 3 units volume of methane can be dissolved in 100 units volume of water. That is why biogas can be generated under water and be collected when water is let out.

Critical Temperature and Pressure1： The average critical temperature of standard biogas is -37 ℃ and the average critical pressure is 56.64×105 Pa (56.64 atmospheric pressure). This explains why the liquefaction conditions of biogas are very demanding. Therefore biogas can only transmitted through pipelines and cannot be traded as an energy commodity by means of liquefaction and canning.

Molecular Size and Structure： The molecular structure of methane is a carbon atom and four hydrogen atoms in a tetrahedron with four equilateral triangles. The molecular weight is 16.04 and its molecular diameter is 3.76×10-10 m, or about one forth of the porosity of cement mortar, which is an important reference for developing composite coating to enhance the tightness of methane tank.

Combustibility： Methane is a high-quality gas fuel. One unit volume of methane requires two units volume of oxygen in order to be completely combusted. As oxygen takes up about a fifth of the air and that 60%～70% of the biogas is methane, one unit volume of biogas requires 6 to 7 units volume of air for full combustion. These are important reference for the development and application of biogas devices.

Explosive Limit Under normal pressure, the critical explosive mixture of standard biogas and air is 8.80%～24.4%. Therefore, in a closure, a mixture of 1 unit biogas and 10 units air can produce a great pushing power from combustion. That is why biogas can be used as a power fuel besides cooking and lighting.

1.2. Principle of Biogas Fermentation

Biogas fermentation, also known as anaerobic digestion, anaerobic fermentation or methane fermentation, refers to a complex biochemical processes under favorable conditions of moisture, temperature and absence of oxygen, in which the organic materials (such as manure, straw, weeds, etc.) are decomposed by a wide range of micro-organisms with various functions, generating a gas mixture of methane, carbon dioxide and other gases.

In nature, the fermentation is a process of metabolism and energy conversion. Through the decomposition process, micro-organisms obtain energy and substance in order to meet the need of growth and reproduction, turning most wastes into methane and carbon dioxide. A wide range of organic substances are continuously degraded in metabolism processes, forming an important part of the material and energy cycle in nature. Scientific measurement and analysis show that about 90% of organic material is converted into biogas, and that about 10% is consumed by micro-organisms themselves. So, it is through a series of complex biochemical reactions that the

1Critical temperature and critical pressure refer to those under which a gas turns into liquid.


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biogas is generated from the fermenting materials. It is generally believed that the fermentation process can be roughly divided into three phases, i.e. hydrolysis phase, acidogenic phase and methanogenic phase.

1) Hydrolysis Phase of Fermentation

Usually solid organic materials cannot be devoured by micro-organisms for their use. They must be hydrolyzed into smaller molecules (such as simple sugar, amino acids, glycerol and fatty acids) under the influence of extracellular enzymes and surface enzymes (such as cellulose, protease and lipase) excreted by aerobic and anaerobic organisms. After this process, the soluble substances with smaller molecular weight can enter the micro-organisms.

2) Acidogenic Phase

In acidogenic phase, under the action of cellulose bacteria, protein bacteria, fat bacteria and pectin bacteria entoenzyme, various soluble substances (e.g. simple sugars, amino acids and fatty acids) are further broken down into low molecular weight substances (such as butyric acid, propionic acid and acetic acid) and simple organic substances (such as alcohols, ketones and aldehydes). At the same time are also released hydrogen, carbon dioxide, ammonia (NH4) and some other inorganic substances. But at this stage the main product is acetic acid (more than 70%), so it is called the acidogenic phase. The bacteria involved in this phase are called acidogenic germs.

3) Methanogenic Phase

In this stage, acetic acid and other simple organic substances generated from the second phase are being degraded into methane and carbon dioxide under the influence of methanogenic bacteria, whereas the carbon dioxide can also be reduced to methane under the action of hydrogen. This stage is called gas-producing or methanogenic phase.

1.3. Conditions for Biogas Fermentation

1) Optimal Carbon-Nitrogen Ratio

For micro-organisms, the raw materials of biogas fermentation are the material basis for survival; they are also the nutrients for micro-organisms to live and generate biogas. According to their physical form, the raw materials of fermentation are divided into two types: solid materials and liquid materials; according to their nutrient composition, they are divided into nitrogen-rich materials and carbon-rich materials.

Generally, nitrogen-rich materials refer to manure of people, livestock and poultry. These substances, through digestion in the gastro-intestinal system of humans and


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animals, are always of small particles, containing a large number of low molecular weight compounds, and the unassimilated intermediate products are water-rich. Therefore, even without pre-treatment, these materials are easy to be degraded through anaerobic decomposition, and the gas-producing process is relatively short.

Carbon-rich materials refer to remnants of straw and other crops, which are rich in cellulose, hemicellulose, pectin, and recalcitrant lignin and plant wax. Carbon-rich materials, with looser texture and smaller specific gravity, usually contain more dry materials than the nitrogen-rich materials. Once inside the fermentation tank, such carbon-rich materials are apt to form a floating shell, and therefore pre-treatment is needed before fermentation. Anaerobic decomposition of carbon-rich materials is slower than that of the nitrogen-rich materials, and the gas-producing cycle is relatively long.

Nitrogen is an important substance of the cytoplasm of micro-organisms. Carbon not only forms the cytoplasm of micro-organisms, but also provides energy for their life activities. Raw materials with different carbon-nitrogen ratios often have different gas-yields. From the aspect of nutrition and metabolism, the fermentation bacteria consumption of carbon is 25-30 times as fast as that of nitrogen. Therefore, while other conditions are met, a favorable carbon-nitrogen ratio for efficient fermentation is 25-30:1. An imbalanced ratio will affect gas-production and microbial activity. Therefore, in order to produce biogas, a reasonable carbon-nitrogen ratio is as important as sufficient raw material. Table 1 shows the optimal carbon-nitrogen ratio of biogas fermentation materials available in rural area.

Table 1 Carbon-nitrogen ratio of biogas fermentation materials

Materials Carbon-material ratio（%）

Nitrogen-material ratio（%）

Carbon-nitrogen ratio

Fresh cow dung 7.30 0.29 25：1 Fresh horse dung 10.0 0.42 24：1 Fresh pig dung 7.80 0.60 13：1 Fresh sheep dung 16.0 0.55 29：1 Fresh human manure

2.50 0.85 2.9：1

Poultry dung 25.5 1.63 15.6：1 Dry wheat stalk 46.0 0.53 87：1 Dry rice stalk 42.0 0.63 67：1 Maize stalk 40.0 0.75 53：1 Tree leaves 41.0 1.00 41：1 Green grass 14.0 0.54 26：1


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2) High-Quality Fermenting Strains

Biogas fermentation micro-organisms are internal factors for artificial production of biogas, without which, all the external conditions cannot work. Therefore, a prerequisite for biogas fermentation is to acquire large amounts of inoculum of such organisms or content-rich strains.

Biogas fermentation micro-organisms are all from nature, while the main part of methane fermentation micro-organisms is methane-producing bacteria, which can be found in any anaerobic conditions with organic materials. Their habitats, or the main sources of inoculum, are as follows: lakes, marshes, bottom of ponds, dung pits, animal faeces and intestines, and drains of slaughter-houses, breweries and bean factories, as well as artificial anaerobic digestion devices.

3) Strict Anaerobic Condition

Methane-producing bacteria, the core microbial flora of biogas micro-organisms, are anaerobic bacteria, which are particularly sensitive to oxygen. Their growth, development, reproduction, metabolism and other life activities all take place without air. Oxygen can inhibit their life activities, or even kill them. Methane-producing bacteria can only live and grow in strict anaerobic environments. Therefore, the biogas fermentation tank must be strictly airtight and watertight. This is not only for the collection and storage of biogas, but also to ensure a good living condition of anaerobic micro-organisms for biogas-production.

4) Suitable Temperature for Fermentation

Temperature is an important an external condition for biogas. A favorable temperature can help the germs grow well and decompose wastes actively and generate methane quickly and productively. In the sense, temperature is the key factor for biogas production.

It is observed that biogas can be normally generated at the temperature between 10～60 ℃. If the temperature is below 10 ℃ or above 60 ℃, the micro-organism cannot live and reproduce well, thus affecting gas-production. Within this range, the higher the temperature, the more active micro-organisms are and the more biogas they produce. Micro-organisms are also very sensitive to temperature change. A sudden rise or plunge of temperature can affect their life activities, so that gas production has been worsened.

Usually, the suitable temperature for fermentation is divided into three bands, i.e. 46～60 ℃ as the high-temperature fermentation band, 28～38 ℃ as medium-temperature fermentation band, and 10～26 ℃ as normal-temperature fermentation band. Biogas digesters in rural areas mainly rely on natural temperature, belonging to


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normal-temperature fermentation. Although the normal temperature band has a wide range, within that, the high the temperature, the better the gas-production. This is why the yield of biogas pool is high in summer (especially in July) and low in winter (especially in January). In rural areas, it is emphasized that warming measures must be taken to ensure normal gas-production in winter.

5) Appropriate pH Level

The growth and reproduction of biogas micro-organisms require a neutral or slightly alkaline pH of the fermentation materials; an up or down pH holds back gas production. Experiments show that biogas can be generated between 6 and 8 of pH value, that peak yield is between 6.5 and 7.5, and that beyond 6 and 9 no biogas is produced.

During the continuous fermentation, some organic acids are neutralized by ammonia produced through ammonification. At the same time, some volatile acids are converted into methane and carbon dioxide under the action of methanogenic bacteria, so that the pH level gradually rose to normal. Therefore, in the normal fermentation process, the pH value in a digester can be mediated automatically: It firstly declines and then rises, and finally reaches the natural equilibrium (a suitable pH level) without artificial adjustment. Only unsuitable ingredients or mismanagement can obstruct normal fermentation, resulting in massive accumulation of organic acids and over-acid phenomenon. If this phenomenon occurs, we should remove some of the liquid and add the same amount of inoculum, to make the accumulated organic acid converted to methane. Another method is to add an appropriate amount of plant ash or lime solution to neutralize organic acids, to restore the pH value to a normal standard.

6) Moderate Concentration of Fermentation

The load of digester is commonly denoted by volumetric organic load, i.e. the amount of organisms being borne by one unit volume of digester per day, usually taking kgCOD/(m3·d) as a unit. Volume load is an important parameter in designing and operating digesters. It is mainly determined by the amount and activity of anaerobic activated sludge.

The load of digester is usually reflected by the concentration of fermentation raw materials. The appropriate concentration of dry matters is 4 ％～ 10 ％ . The concentration varies with temperature: about 6% in summer and 8% to 10% in winter. Either an over-high or over-low concentration is not conducive to methane fermentation. An over-high concentration means that the moisture is too low, which is not good for the decomposition of raw materials. It also causes a massive accumulation of acidic substances, which is not good for the growth and reproduction of methanogenetic bacteria and thus affects the normal gas-production. An over-low concentration, namely too much water, means that the content of organisms is relatively low in unit volume. It also means low gas production and insufficient utilization of the digester.


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7) Toxic Substances

In normal circumstances, agricultural residues do not contain a large amount of toxic substances. But pesticides can enter manure and sewage during animal epidemic prevention and disinfection on domestic stock farms, and industrial organic sewage often contains toxic substances. These harmful substances, including inorganic and organic materials, can interrupt or inhibit the fermentation process.

The so-called "toxic" is a relative term. At a very low concentration, a toxic material may play a catalytic role, but above a certain concentration, the same substance can inhibit fermentation. The inhibitory concentrations of different substances are not the same. For example, 1mg/L of heavy metal salt plays a catalytic role in promoting biological activity. When the concentration rises beyond the optimal concentration, the promoting function begins to decline. When the concentration increases to a critical point, the biological activity becomes lower than that in the absence of this substance, which shows the toxic effect of the substance.

Most heavy metals, including their organic and inorganic salts, have very strong toxic effects, such as mercury, silver, lead, zinc, copper, etc. This is because they are mostly protein precipitation agents. If such a heavy metal is combined with protein or enzyme, it will cause enzyme variation, inhibition of reaction, or even death of the cells. Experiments indicate that if the concentration of heavy metal salts causes less than 20% reduction of gas production, this concentration is acceptable.

2． Operation of Large- and Medium-Scale Biogas Projects

2.1. Technology of Large- and Medium- Scale Biogas Projects

A complete large- or medium-scale biogas project, regardless of its size, basically includes the following units: raw materials (waste water) collection, pre-treatment, digester, post-treatment, biogas purification and storage (As is shown in Figure 1). According to the digester type and fermentation temperature, biogas fermentation technologies can be divided into different types.

Fig. 1 Technological process of biogas fermentation


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2.2. Introduction of Individual Unit of Biogas Project

1） Collection of Raw Materials

Adequate and stable supply of raw materials is the basis for anaerobic digestion process. A number of biogas projects are forced to stop operation or abandoned because of changes in the sources of raw materials. In practice, collection methods directly affect the quality of raw materials. For example, if a pig farm uses automated washing, the total solid concentration in sewage can only be 1.5%～3.5%; if manure scrapers are used, the concentration will be 5%～6%; and if manure removal and transportation are handled by man, the concentration may reach 20%.

As a rule, the collected raw materials are to be stored in an adjusting tank. As the collection time is relatively concentrated, but that the digester feeding should be evenly distributed in the day, the adjusting tank should be large enough to contain raw materials for 24 hours’ consumption. In warm seasons, the adjusting tank can often play the role as an acidification tank, which improves the digestibility of raw materials and accelerates the anaerobic digestion. But if the retention period of raw materials is too long the adjusting tank, the biogas-production will decline as a result of aerobic respiration and fermentation.

2） Pre-treatment of Raw Materials

Raw materials are often mixed with a variety of debris. In order to deliver the materials through pumps, to prevent failure in the fermentation process, and to adjust the solid concentration all the while, the pre-treatment of raw materials is necessary. During the pre-treatment, long grass in the manure of cattle and pig and feathers in the chicken manure should be removed. Otherwise, they may easily obstruct pipelines. The shell and gravel in chicken manure are to be removed by sediment. Otherwise, they will soon settle in the digester at the bottom, which is then not only difficult to remove, but also reduces the effective volume of the digester. Table 2 shows the properties and gas-yield of different animal manures.

Table 2 Properties and gas yield of different animals

TS％ Potential gas yield

(m3／kgTS) Materials

Range Typical value

Range Typical value

Special features

Fresh cow dung

15～18 18 0.18～0.30 0.25 Much grass, little sediment; more floating debris than deposits.

Fresh pig dung

18～25 20 0.25～0.45 0.30 Much sediment in winter; more deposits than floating debris.


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TS％ Potential gas yield

(m3／kgTS) Materials

Range Typical value

Range Typical value

Special features

And vice versa in summer. Fresh

chicken dung

25～40 30 0.30～0.55 0.35 With feather and shell deposits; sediment being difficult to remove.

3） Anaerobic Digester

Anaerobic digester is the central equipment in large- and medium-scale biogas projects. Nowadays, the widely used digesters in large- and medium-scale biogas projects are the Upflow Solids Reactor (USR), the Completely Stirred Tank Reactor (CSTR) and the Piston Flow Reactor (PFR).

The USR is for the fermentation of animal manure with high suspended solids. In this reactor, through natural sedimentation in upflow fluid state, the solid particulate matters in animal manure and fermenting micro-organisms can stay in the digester for a long time, increasing the rate of gas-production. In Beijing, USR technology was first used in Liuminying, Liulihe Third Street and Nanhanji projects, which use poultry and pig dung as fermenting materials. The biogas generated is used as cooking fuel for hundreds of local households, and the residue is for farmland use. Till now, these installations have been successfully operating for a decade.

The CSTR is a typical conventional digester used in sewage treatment, in which the inflow and outflow of the materials keep dynamic homoestasis, the liquid, solids and micro-organisms are mixed in fermentation broth, and the concentration of effluent organic materials is equal to that of the materials in the reactor. CSTR technology is suitable for liquid waste with high suspended solids of high concentration and temperature. It is widely used in ethanol wastewater treatment. In 1999 the largest set of CSTR anaerobic fermentation tanks of ethanol wastewater treatment was built in Taichang, Jiangsu, operated by Xintai Alcohol Co., Ltd. The total volume of this tank group has reached 13,200 cubic meters, processing cassava dry waste of nearly 2,000 cubic meters and producing more than 40,000 cubic meters of biogas everyday. And the largest single tank with a volume of 5000 cubic meters was built in Henan by Nanyang Alcohol Plant.

The PFR is a rectangular non-completely mixed digester, in which the raw materials enter from one end and move out of the other in the manner of a piston. Inside the digester, because of the generation of biogas, vertical mixing is significant, while little horizontal mixing takes place. The hydrolytic acidification is significant in the feeding end. As the mixture approaches the outlet, the biogas generation is intensified. In this system, since the inoculum is inadequate in the feeding end, the back-flow of solid materials is necessary. To prevent micro-organisms from being washed out, a


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baffleplates should be set in the digester for operation stability.

4） Post-treatment of Fermented Materials

For large-scale biogas projects, the post-treatment of discharged materials is an indispensable constituent. The post-treatment can take different forms. In the energy and ecological mode, as the post-treatment is a seasonal and inconsistent process, the biogas slurry and residue have to be temporarily stored in appropriate-sized storage pools. In the environment friendly mode, the discharged materials are first let to deposit and then go through solid-liquid separation. Afterwards the solid residue can be used as fertilizer or a component of compound fertilizers. The clear liquid, through standardized in-depth treatment, e.g. aeration tanks, oxidation ponds, artificial marsh, etc., though this means more costly.

5） Purification, Storage, Transmission and Distribution of Biogas

After fermentation, biogas contains a certain amount of hydrogen sulfide and water. Condensation of water can cause pipes plug, and sometimes the gas-flow meter is also filled with water. Hydrogen sulfide can cause rapid corrosion of pipes and instruments, and the combustion of hydrogen sulfide will generate chemical substances harmful to people. Therefore, water and hydrogen sulfide must be removed from the gas in large-scale biogas projects, especially those gas supply projects. In a digester operating at medium temperature (35 ℃), the water concentration in biogas is 40g/m3. At 20 ℃, the water concentration is only 19 g/m3. This means that in every cubic meter of biogas cooled from 35 ℃ to 20 ℃ there will be 21 grams of water condensate.

Biogas contents 1～12 g/m3 hydrogen sulfide. The raw materials with high content of protein and sulfate will generate more hydrogen sulfide in biogas. According to city gas standards, hydrogen sulfide should not exceed 20 mg/m3. The removal of hydrogen sulfide usually takes place in a desulfurization tower with built-in desulfurizer. Because the desulfurizer should be regenerated or replaced after a certain time, there should be two towers at least for alternation. In addition, the bio-desulfurization tower technique is also available, though only applied in extra large biogas projects.

3． Operation Management of Large- and Medium-Scale Biogas Projects

3.1. Management Regulations

1） General Principles of Operation Management

（1） The operation management staff must be familiar with the techniques, equipments, operational requirements and technical indicators.


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（2） The operators must understand the technology of the project, and be familiar with the operational requirements and technical indicators of the facilities on their post.

（3） There should be technology flow diagrams and safety operation instructions on every post, which are shown in conspicuous spots.

（4） Operation management staff and operators should follow the requirement and carefully inspect the operation of installations, equipments, electrical devices and meters. Once observing abnormal situation, the operator should promptly handle it or report to the leaders in charge.

（5） The operators on every post should keep operation record and the recorded data should be accurate.

2） Safety Rules

（1） Strictly abide by safety rules and regulations, as well as all the provisions in the operation procedures.

（2） No fire is allowed. According to the relevant provisions, fire equipments should be provided in the workshops with electrical devices and places with flammable and explosive materials.

（3） Before cleaning or maintaining the constructions (such as collecting tank, anaerobic tank and the sludge pool) with harmful and flammable gas, measures must be firstly taken to ensure ventilation and air replacement. Work can be assumed only when the content of harmful and flammable gas is proven to be in compliance with safety requirements.

（4） While cleaning mechanical and electric equipments and their vicinity, never wipe their rotating parts. When using water, avoid splashing onto cable ends, electrified parts and lubrication spots. It is not allowed to change clothes near running devices.

（5） When work high above the ground is carried out, protective measures must be well taken.

（6） When faults of electrical equipments or circuits occur, the power should be cut off immediately. All the equipments should be repaired in the power-off state, with warning signs hung by the main switch during maintenance.

（7） In raining or snowing weather, operators working or supervising on structures should care about skidding.


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（8） Operators on every post should put on required protective wearing and take safety measures.

（9） The place with harmful gas, flammable gas, odor and moisture must be ventilated.

（10） Work areas and access roads should be kept neat and clean, and any unstable items should not be piled in work areas

3） Shift System

（1） The shift deliverer should inform the shift details clearly and carefully.

（2） If something abnormal occurs during shift exchange, it should be handled by the shift deliverer. If the problem cannot be solved instantly, it can only be passed over with the receiver's agreement.

（3） If an accident occurs, it is in the shift deliverer's charge. If an accident occurs after shift exchange, it is in the receiver's charge.

（4） Details to be informed: number of staff on the shift and their work, parameters of production, the state of equipment and instruments, checking the records of present operation, the consumption of raw materials, working conditions and sanitation, availability of tools and protective stuff, any instruction from leadership.

3.2 Operation Management of Project Units

1） Operation Management of Biogas Fermentation Device

（1） Monitoring of operating parameters：the quantity of materials fed in one day or shift, the temperatures of liquid at feeding and discharging and other sampling points inside the digester, and pH, COD and SS values. Temperature and pH value are to be monitored within every shift. Before the mastery of operation regulation, COD and SS should be monitored every day. When the operation is stable, these parameters can be monitored once several days or weekly.

（2） Guiding operation by monitoring data：According to the various data from monitoring, control the volume of sludge back-flow, volume of feeding materials, their temperature, etc. Tabulate the above-mentioned parameters, and, through making them enter data in the table, urge the operators to monitor the system operation timely and seriously. Analysis of these data can show the trends of pH and temperature, which is an important guidance for system operation.


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（3） Pre-treatment of raw materials: This is the foremost prerequisite for stability of the biogas fermentation digester. The treatment includes sand sediment and removal of large debris and floating scum, raising the temperature of the feeding materials to 3 ～ 5 degrees higher than the normal operating temperature (concerning medium- or high-temperature biogas installations, especially industrial sewage anaerobic fermentation); adjusting the pH value and concentration of feeding materials by supernatant fluid back-flow. The concentration of feeding materials should be below 6%, as can be compared with the sample prepared in advance. The pH value of the feeding solution should be 5～7, according to the sludge volume in the digester. Generally speaking, livestock wastewater can be fed directly, without adjustment of its pH value.

（4） Feeding volume control: A too large volume feeding will easily cause operation acidification or even failure; a too small volume feeding will lead to inefficiency. On the basis of the designed volume, the ideal quantity for every day or every time feeding should be in line with actual operation parameters: that COD removal rate reaches 80%, that the methane content in biogas is above 50%; that the biogas yields a blue flame, and that the pH value of the liquid in the fermentation tank remains about 7.

（5） Post-treatment of discharged liquid: To realize zero-emission, after fermentation, the supernatant fluid can be used as diluter for raw manure, or as surface fertilizer of nutrient solution, or as liquid fertilizer for soil-less cultivation.

（6） The liquid mixing in the digester: In the fermentation tank, liquid should be mixed periodically, according to the designed mixing time and speed. The purpose of liquid mixing is to let the raw materials have full access to the original sludge, to ensure sufficient fermentation and gas production.

（7） Removal of mud in the digester: In the biogas fermentation tank, the mud should be removed periodically. Before the mud-removal, make sure the storage space of the fermentation tank is connected with the atmosphere or the storage holder smoothly. Then open the valve gradually, to avoid negative-pressure in the tank.

（8） Regular cleaning of the digester: During the regular cleaning in the fermentation tank, the entrance holes for staff at the bottom and on the top of the tank should be fully open. After sufficient ventilation, in line with the fire prevention and human safety rules, all the in-tank operation should be carried out under the supervision of others and with security measures. When the digester resumes normal work, follow the preparatory procedures of the start-operation.


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（9） Antifreeze management: Before winter comes, especially in northern regions, carefully prepare for normal operation in the cold season. Carefully check and reinforce the thermal insulation measures for valves, water seal, manholes, condensate water trap, pipelines, gas storage holders, pools, solid-liquid separators, etc.

2） Operation Management of Pumps and Mixers

（1） Carefully read the operating instructions. Operate strictly in accordance with the operating regulations.

（2） Upon operating pumps, strictly enforce the itinerary inspection scheme, and comply with the following requirements:

a. Observe the instruments and meters, making sure they work well.

b. Bearing temperature must not exceed 75℃.

c. Check the pump to see whether the packing gland is hot, and to see whether the dripping is normal.

d. There should be no abnormal noise or vibration in the pumping unit.

（3） Keep the pumps and mixers in good condition.

（4） Operators should keep the pumping station clean, with tools and utensils neat in place.

（5） Promptly remove obstructions at the impellers, valves and pipes.

（6） When a pump is started or is running, operators may not touch the rotating parts.

（7） Do not start the pump frequently.

（8） Stop the pump immediately if any of the following occurs:

a. The pump suddenly makes abnormal noise.

b. Bearing temperature is too high.

c. The reading of voltmeter or ammeter is too low or too high.

d. Leakage occurs in pipes or valves.


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3） Operation Management of Electric Appliances and Monitors

（1） Carefully read instructions for each meter, and strictly follow the operating regulations.

（2） Operators should observe the control signals of every device and system and record the readings. If failure occurs, notify the maintenance or operation management staff immediately.

（3） Inspect the control apparatus and record display in due time. On seeing abnormal situations, take measures immediately.

（4） Clean out dirt on the sensors, transmitters and converters of every instrument.

（5） When an instrument fails, do not arbitrarily change the preset monitoring spot or remove the transmitters and converters.

（6） All the control instruments and equipments in the control room should be working under the required voltage.

（7） When there is any malfunction alert or protective trip, cut off electric power immediately. Maintenance must be taken in the OFF state. The power must be kept off till the failure is resolved.

4） Operation Management of Solid-Liquid Separators

（1） Carefully read equipment manuals and follow the instructions for adjustment, operation and maintenance.

（2） The trial of solid-liquid separators should be run before they are loaded.

（3） Solid-liquid separators at work should be regularly checked. Adjust water feeding according to water quality.

（4） In order to maintain optimal working conditions of separators, regulate the operating parameters of equipments according to the moisture content of the solids after separation.

（5） Clean the solid-liquid separator during shift break.

（6） Do not touch the rotating parts of the working solid-liquid separator.

（7） Instant maintenance is needed when abnormal phenomenon occurs in a running solid-liquid separator.


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（8） Repairing must be carried out in the OFF state.

5） Operation Management of Pre-treatment Pool and Digester

（1） The adjusting tank and the acidification heating tank are means of pre-treating materials to be fed into the anaerobic fermentation digester. Their liquid level should be maintained at the designed level.

（2） Regularly check the working condition of the scum remover.

（3） Regularly remove sludge according to the requirement, and close the valve shortly afterwards.

（4） The skimming of scum and the cleaning of weir rims should be carried out under supervision with safety measures.

（5） Maintain good ventilation about the gate wells and corridors connected with mud pipes.

6） Operation Management of the Gas Storage Holders, Purification Facilities and Transmission Pipelines

（1） The key point of gas-holder operation management is to prevent air leakage. For the operative gas-holders approved through leakage check, the explosion-proof rubber sheet on the floating cover should be regularly changed and the aging preventive shield should be added over. For the model of wet gas storage holders, regularly check the water level in the tank and in the water-seal, to prevent leakage caused by lack of water. Inspect the surface of the holder and paint the steel bell jar on a regular basis, to prevent leakage through pores in the shell caused by corrosion.

（2） About gas replacement in the holder: Before starting the storage holder, gas replacement must be carried out, which may assume direct replacement with biogas or indirect replacement using inert gas, e.g. N2, CO2, etc. The flue gas components are mainly nitrogen and carbon dioxide, which can act as an economical replacement media. It should also be noted that an inert gas with a larger specific gravity is suitable for replacing a flammable gas with a smaller specific gravity, whereas an inert gas with a smaller specific gravity is for replacing a flammable gas with a larger specific gravity. Replacement should be carried out in accordance with the operational procedures. Safety must be ensured.

（3） Periodically measure the volume and pressure of storage, and take records. The pressure of holders should be maintained under the safe pressure for normal operation.


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（4） For the model of wet gas storage holders, the water-seal should be kept at the required level. In summer fresh water should be added in due time, and in winter anti-freezing measures should be taken when the temperature is below 0℃.

（5） The condensed water in gas pipes and collectors should be discharged regularly. Prevent biogas leakage during water discharging.

（6） Periodically regenerate or replace the desulfurizing agent in the desulfurization device. Anti-freezing measures should be taken when the temperature is below 0℃ in winter.

（7） Water level in the water-sealed can should be maintained at the standard height, with timely discharge or addition according to the liquid level.

（8） When personnel move about or up and down the storage holders to do supervision, operation or maintenance, they must take measures to prevent the generation of static electricity. Staff should never wear high-heels or shoes with nails.

（9） The maintenance of biogas holders should be carried out by licensed professional staff with safety plans concerning the working procedure. Before letting out water in the seal, the outlet valve in the floating cover must be opened first, to prevent the cover from distortion due to negative pressure.

（10） In winter, measures should be taken to keep the water-sealed tank and drainage valves from freezing, in order to prevent negative-pressure or super-pressure upon the floating cover.

（11） Fire insulators should be installed in the inlet and outlet pipes and deflating valves, and be taken out and cleaned at a regular basis.

（12） Every year before the thunderstorm season, the lightning rod over the gas holder must be checked, fixed and measured, making sure that the electric resistance to the ground is less than 10 ohms.

3.3 Safety Management of Project Units

1） Items for Daily Safety Management of the anaerobic digester:

（1） Daily observe the inflow and outflow of water of the anaerobic digester, to see whether it is normal.

（2） Observe the top seal ring, to see whether it leaks gas or material. If there is leakage, check whether the outlet pipe or biogas pipe is blocked.


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（3） Periodically add water into the water-sealed ring to supplement the loss of moisture caused by evaporation. Prevent icing of water in the water-sealed ring.

（4） No smoking, electrical cutting or gas cutting are allowed around and on top of the anaerobic digester.

（5） Periodically inspect the corrosion state of the operative body, railings and other metal components of the anaerobic digester. Apply preservatives promptly.

（6） Periodically check the anaerobic digester to prevent corrosion and damage to the equipments inside the tank.

2） Daily safety management of storage holder

（1） No smoking, fire or gas-test are allowed near the storage holder.

（2） Daily check the pipes and valves around and associated with the storage holder. If there is any leakage, it must be resolved instantly. When a storage holder is to be reused, a tightness test is a must before it is taken as qualified.

（3） The wheel axle should be lubricated every six months to keep the wheels rotating freely. Check to see if the vertical movement of the holder is blocked. If it is, find out the cause and resolve the problem as soon as possible.

（4） When the digestive system stops running, the gas storage holder should be fully evacuated. No air is to be stored in it while the system is off.

3） Technical points concerning transmission and distribution safety

（1） Pressure control: As an important parameter for stable operation of the biogas system, pressure must be observed from time to time. Any abnormal condition calls for immediate examination. When pressure increases, check whether there is blockage inside the pipes, water in the condenser or icing of the water, curdling of agent in the desulfurization tower, or obstruction to the gas holder, which should of course be resolved instantly. When pressure decreases, check where there is rupture or leakage in the pipes or biogas devices, i.e. the gas holder, desulfurization tower, vapor-water separator, etc.

（2） Fire stopping inside biogas pipes: If there is a negative pressure in the biogas system, back firing may occur inside biogas pipes, which may boost temperature and expand gases, causing damage to the pipes and equipments, or even leakage and explosion. Therefore, routine check of the flame arrester in the biogas piping must be emphasized. For the wet type of flame arrester,


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regularly check the water level of the water-sealed holder and timely make up for evaporation or loss of moisture with the biogas. The height of water seal should be controlled within a range of 50 to 100 millimeters. For the dry type of flame arrester, the wire net should be periodically taken out and cleaned, in order to minimize its resistance to ventilation. What is more, if there is too much filth on the net, its heat absorbing rate and efficiency will be lowered, as affects its fire-stopping function.

4． Maintenance Management of Biogas Project

4.1 Maintenance of Facilities

The regular maintenance of all facilities and equipment in a biogas project is a necessary condition for normal operation of the project. In large- and medium-scale biogas plants, the devices that need maintenance can be divided into several parts, i.e. electrical installations, testing instruments, operative power devices, non-operative fixed facilities, gas and liquid transmission system, etc.

4.2 General Principles of Maintenance

1） The operation management staff and maintenance staff should be familiar with the maintenance requirements of mechanical and electrical equipments.

2） Regularly check and maintain the structure of constructions, various valves, guardrails, ladders, pipes, supports and covers. Repair or replace any damaged lighting equipments.

3） Regularly check and tighten all kinds of connecting parts of devices, and periodically replace the worn parts of the shaft couplings.

4） Regularly inspect and clean the electric control holder, and test its various technical performances.

5） In addition to routine maintenance of the mechanical equipments, also check and fix the devices in accordance with the requirements of their designer or producer.

6） Pipes and open channels connecting the structures should be cleaned up once a year.

7） The testing, maintenance and cycle of the lighting evasion and explosion prevention devices of all the buildings and structures should comply with the regulations set by the authoritative sectors in charge of electricity industry and fire prevention.

8） Carefully operate and maintain the anaerobic reactor, to ensure its stable


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operation.

9） Carefully manage and maintain the gas storage holders, to ensure their stable operation.

10） Periodically inspect the pressure in the anaerobic reactor, gas storage holders and biogas pipelines, in order to prevent over-pressure and negative-pressure.

11） Timely discharge the condensate water inside the condenser.

12） Regularly clean the flame arrester and filters.

13） Periodically replace the desulfurization agent in desulfurization towers, to make sure the content of hydrogen sulfide in biogas below 20 mg/m3.

14） Periodically check the corrosion state of gas holders, biogas pipelines and other equipments, and promptly treat them with preservative.

4.3 Maintenance of Electrical Instruments and Meters

1） Points for maintenance of control panel:

（1） Screens should be kept clean, without dust or dew on them.

（2） Relay contact points should be regularly checked and replaced. Regularly test its process control systems.

（3） The callipers at cable terminals should be regularly checked, to ensure close contact and no corrosion.

（4） After maintenance, the cables should be arranged neatly and classified clearly.

2） Maintenance of instruments and meters:

（1） Keep the components clean and rustless, keep the dial gauge of meter panels clear, keep the nameplates, tags, seals intact, and regularly inspect and replace damp-proof agents.

（2） Clean the parts with alcohol, cleaning agents or ultrasonic means. Never use agents harmful to instrument parts.

（3） Regularly check and fix the components, probes, converters and calculators in the instruments and meters.


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（4） The repairing of meters should be down by professional staff. As for the repairing of expensive instruments, contact specialized department or their manufacturer. Never disassemble them arbitrarily.

（5） The checking of meters and instruments listed in compulsory state supervision should be delivered to the authoritative department.

（6） The checking of the ground connection wiring of meters, instruments, electrical control holders and lightning rod of gas storage holder should be done by licensed electricians regularly, to prevent disconnection of ground wiring, false connecting or too large electric resistance, as may cause accident in thunder storms.

（7） The maintenance of major expensive instruments and meters must be carried out according to the instructions by the manufacturer. Once with problems difficult to distinguish, contact the after-sales service for maintenance.

4.4 Maintenance of Pumps

1） The daily maintenance of pumps should comply with the instructions of the products.

2） Check the seal of the filler or oil, and add or replace filler, lubricating oil or grease according to needs. Check whether fixers are loose.

3） Check, adjust and replace the valves of pumps one time every half a year. Check the water tank and impellers according specific requirements and remove the debris in the pump at least one time every half a year.

4） Check the level, quality and temperature of the oil about the bearings. The bearing lubricator should be replaced regularly; lubricating oil to be replaced after 500 hours’ work and lubricating grease after 2000 hours.

5） The alternative pump should be run for trial at least once a month. When ambient temperature is below 0 ℃, water must be let out from inside the pump shell.

4.5. Maintenance of Warming Installations

1）Maintenance of Boilers

（1）Between every 3 to 6 months boilers should be shutdown for examination and scale removal. Pay attention to seams and corrosion of steel shell for any problem.

（2）The outer shell of boiler should be painted every year.


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（3）Idle boilers should also be maintained with either dry or wet methods. If idling for more than a month, a boiler can be maintained in the dry method: clear the inside of the boiler, heat it with slow fire, put inside plates of small peace (10-30mm) quicklime, making sure the quicklime be not in touch with the metal cylinder. Then close all the openings to the outside. In every three months check to see if the quicklime has turned into dust, and replace it if so. When the boiler is to start again, take the quicklime plates out. If a boiler is to stop for a short time, the wet method is suitable: thoroughly clean the inside of the boiler, add in treated water, and heat it till about 90℃. Keep the temperature for one hour or two to drive out the moisture from the boiler, and then shut all the connection with the outside. Note: the wet method should not be used in winter.

2）Maintenance of the solar heating system

（1）Regularly remove dirt to prevent obstruction of pipes. Wash the tank to guarantee water quality. When removing dirt, so far as water inlet is normal, just open the dirt valve till clear water runs out.

（2）Regularly wipe out the dust and dirt on the transparent solar heat collecting board, to guarantee its rate of transparency. The cleaning should be done at dawn or dusk when sunlight is not strong and temperature is low, in case the transparent board should be cracked by cold water.

（3）Check to see if the transparent boards are intact, and replace those damaged in time.

（4）For the type of vacuum tubular solar collector, regularly check the vacuum state or fracture of inner glass tubes. When the barium-titanium air absorption agent turns black inside the vacuum tube, it means the pipe's vacuum is reduced and the heat collecting pipe should be replaced.

（5）In addition to cleaning the vacuum tubes, also clean the reflector board.

（6）Conduct itinerary check pipes, valves, floating ball valves, electric-magnetic valves and connecting hoses for any leakage, and do timely repair.

（7）If there is any damage or fall-off of painting on heat collectors, mend it up instantly. All the piping and scaffolding should be painted every year to prevent corrosion.

（8）Avoid stagnate heating. Stagnate heating happens when the circulating system is stopped, with the effect of raising the inner temperature of the heat collector, damaging the painting layer, warping the holder's insulation layer, or even cracking glass pipes. The reason might be obstruction in circulation piping. In the natural circulation system, the cause might be the shortage of cold water supply or the low


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water level in hot water tank which is below the circulation tube. In the forced circulation, it may be due to the stop of circulating pump.

（9）For the all-weather hot water system equipped with auxiliary heating source, the heater and exchanger should be regularly checked to guarantee normal working. Never use the auxiliary heater with electric heating tube, until its electric leakage protector is checked in advance. For the solar heating system with heat-pump, also check the heat-pump compressor and fan. Problems with any device must be timely resolved.

（10）For the plate-type system, water must be let out of the heat-collector when the atmospheric temperature is below 0℃ in winter. If the system is equipped with compulsory anti-freezing circulation system, just start the system without letting out the water in the heater.

4.6 Maintenance of Solid-Liquid Separators

1） Regularly maintain the solid-liquid separator and add lubricating oil or grease according to the operating instructions.

2） When failure or damage occurs in the solid-liquid separator, timely repair it or replace the damaged parts. No operation is allowed before problem is solved.

3） The solid-liquid separator should not be run under overload. Once there is short circuit or protective trip in the electrical control holder, it should be re-closed only after troubleshooting.

4.7 Maintenance of Operative Units

1） Maintenance of adjusting tanks, acidification heating pools and collecting pools:

（1） Regularly clean the pipelines between pools.

（2） Adjusting tank should be regularly evacuated, and the accumulated sand should be cleared regularly. Check and repair the measuring devices and scum removal devices periodically.

（3） Once operation is normal, the mud should be cleared regularly. Frequently check the mud valve and carry out maintenance.

2） Maintenance of gas storage holder

（1） Periodically check the biogas holder, biogas piping and valves for any leakage.


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（2） Periodically recoat the painting on the biogas storage holder.

（3） Regularly check the lifting device of the biogas holder and the valves, and added lubricating grease.

（4） In cold areas, the antifreeze facilities of the water seal in the biogas holder should be checked and repaired before winter comes.

（5） The water stored in the gas storage holder must be replaced once a year.

（6） After 3 to 5 years' operation, the biogas storage holder should be thoroughly maintained. All the valves should be replaced when expired.

（7） The biogas alarm device should be checked and verified regularly.

（8） Periodically replace the safety rubber sheet of the floating cover. Avoid its aging caused by direct solar radiation.

3） Maintenance of anaerobic fermentation tank:

（1） Anaerobic fermentation tank, connecting pipes and valves should be inspected and maintained regularly.

（2） Regularly clean and ventilate all the heating facilities of the anaerobic fermentation tank.

（3） If a heat exchanger is used, the sealing materials at the piping and valves should be replaced regularly.

（4） If the propeller is used for mechanical agitation, the bearings should be regularly inspected and lubricated, and the connecting bolts of the scaffolding should be periodically checked and tighten.

（5） The insulation and anti-freezing measures should be well taken in winter. Pay particular attention to the anti-freezing measures for overflow pipes and explosion prevention devices.

（6） The anaerobic fermentation tank should be thoroughly cleaned, checked and repaired after 3 to 5 years' operation.

（7） After normal operation for a year, properly wash out the debris (but prevent the loss of bacteria sludge), and clean-up the sediment on the overflow weir on the top.

（8） It is better to use an anaerobic fermentation tank which has no moving parts


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inside and which is heated by outside devices.

（9） The repair and maintenance of the underground fermentation tank may refer to the above requirements properly

4） Maintenance of gas and liquid transmission system

（1） Regularly replace or regenerate the desulfurization agent in the desulfurization tower, to reduce resistance to the biogas system.

（2） Keep the water level at the standard line in the water sealed tank. The excessive water should be let out in time. The seal water in the tank should be replaced every six months. Keep the water level clear and transparent.

（3） Regularly discharge the accumulated water from viper pipes, biogas pipes and condensate water collector, in order to keep the transmission piping fluent and minimize transmission pressure loss.

（4） Ensure that the valves of gas and liquid transmission pipes can be turned on and off freely. If there is damage, repair or replace instantly.

（5） Before winter comes, carefully check the heat insulation measures for gas and liquid transmission pipes. Damaged parts must be repaired in time.

4.8 Other Considerations

The routine maintenance of large- and medium-scale biogas installations needs expertise of mechanical fitters, electricians and instrument technicians. Biogas project management staff should be able to foresee any possible accident, judge the reason and location of the problem once abnormal conditions occur, and solve simple problems. When faced with major problems or technical troubles with meters and instruments, inform professional staff for timely maintenance. Rash actions should not be taken.

5 Security

5.1 Danger Source

1）Biogas suffocation

In the air there is about 0.03％～0.1％ carbon dioxide and 20.9％ oxygen. When carbon dioxide increases to 1.74％ , people’s breathing will be quickened and deepened. When carbon dioxide increases to 10.4％, people can bear it only 30 seconds. When carbon dioxide increases to 30％, people’s breathing will be inhibited till loss of sense and death. In terms of oxygen, when it falls to 12%, people’s


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breathing will be quickened. When oxygen falls to 5%, people will suffer loss of sense. If one enters an environment of only 4% oxygen from a normal atmosphere, it takes one only 40 seconds to loss consciousness and stop breathing. In the digester, there is only biogas without oxygen, where carbon dioxide takes up 35%. Therefore in such a condition, people can quite easy suffocate. If the digester contents phosphorus bearing fermenting materials, they will generate virulent gas of hydrogen phosphide ( PH3), which can kill a person instantly.

2）Biogas explosion and fire

In biogas, methane is a flammable and explosive gas. When methane takes up 5% to 15% volume in the air, it will explode once in contact with flame or heat above 700℃. When biogas is mixed with more than two times of oxygen, it will burn once in contact with flame or heat source above its ignition point, as is fire hazard.

3）Hydrogen sulfide intoxication

Hydrogen sulfide is a poisonous gas, its toxic dose is shown below:

2000ug/L Immediate death.

600～1 000ug/L Death within 30 minutes.

500～700ug/L 30 ~ 60 minutes of exposure may cause serious disease.

50～100ug/L Over 60 minutes of exposure would cause bodily disability.

Before desulfurization, biogas usually contains 200～500ug/L hydrogen sulfide, or even as high as 1000 ug/L. If there is a large amount of biogas in the air, in addition to direct hydrogen sulfide intoxication, the suffocation caused by lack of oxygen can increase its toxicity.

4）Shock

Electric shock accidents often happen out of touch with electrified outer cover of the devices. Electric current of more than 50 mA through the human body is mortal. The injury degree is related to the amount of electric current and the length of time. The longer the time, the greater the risk. The most serious harm happens if the current goes through the heart or central nervous system. The current through the heart can cause ventricular fibrillation, and the current through the central nervous system can cause serious disorder which may lead to death.

5.2 Danger Prevention Measures

1）Prevention of Suffocation, Explosion and Intoxication


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（1） Management staff must operate the system in strict accordance with the safe operation provisions, conduct safe production, and be prudent in management.

（2） Management staff must administer and maintain the devices strictly according to the provisions in the instruction manual, in order to guarantee normal operation.

（3） Naked flame and smoking are strictly forbidden. No steel tool colliding, electric welding or gas cutting operations are allowed in the vicinity of the biogas system.

（4） Establish the access control system, and strictly forbid children and idle staff. Lighters and other dangerous stuff are strictly prohibited.

（5） No management staff is allowed to enter operating units containing biogas, such as the covered collecting tank, covered acidification adjusting tank, anaerobic pool (tank) or gas holders. The maintenance of these structures should be strictly in accordance with the safety procedures.

（6） Periodically inspect the tightness of the biogas piping system and biogas devices. If leakage is found, cut off the gas and repair it promptly. After the maintenance of piping and storage devices is completed, an airtight test is a must before restarting the system. No buildings or obstructions should be set on the ground above the main pipes, and no heavy trucks are allowed to pass. The prevention of biogas leakage is the fundamental measure of safety operation.

（7） If a biogas device should be let out because of accident, the releasing must be done intermittently. Never let out the biogas once out of the container. The release should also be done in fine weather. If there might be thunderstorm or lightning, it must be stopped. Besides, watch for any naked fire or heat source in the lower current.

（8） As hydrogen sulphide and carbon dioxide are heavier than air, beware of the low cavities like the checking well, in prevention of intoxication.

（9） The biogas station must be fully equipped with water tap, extinguishers and fire warning boards. The fire-prevention devices must be checked regularly to ensure normal use.

（10） Before in-pool work is started, the bio-liquid should be discharged till below the level of the material inlet and outlet holes. Thoroughly let out biogas and provide ventilation. To ensure safety, put in some small animals like chicken, duck or rabbit for test before human staff enter the pool.

（11） Where there are staff at work down in the pool, there must be staff over the


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pool for supervision. The in-pool staff must be tied to safety cord, so that they can be instantly rescued in case of danger.

Warning: If someone is found intoxicated, never get down into the pool in haste. Use air-blower or other methods to blow air into the pool to provide fresh air for the victim to breathe in. If, out of ignorance, people rush to the victim, more victims will be inflicted. The rescued victim should be sent to the nearest hospital without further delay.

2）Prevention of Electric Shock

（1）Frequently check electric equipments. If any device is burnt or insulation resistance is lowered, repair instantly.

（2）Maintenance of electric devices in the OFF state must be carried out according to required procedures with strict safety measures. Guard against sudden power supply. Never count on predetermined cut-off.

（3）Electricians must wear insulating clothes and use insulated tools, whose work must be supervised by designated staff with necessary safety measure. Safety distance must be kept from other electric devices.

（4）Work high above the ground must be carried out according to required procedures, including switching power off, checking electric state, installing ground wires, hoisting No On warning board, setting safety railings, etc.

（5）Low voltage power should be used for wet, hot, underground or enclosed working conditions. The low voltage should be acquired from the secondary coil of a transformer, but never by means of resistance or single-coil methods.

（6）In case fire breaks out of electric leakage, cut off electric power first. Use sand or …extinguisher to put out the fire. Never use water or …extinguisher for electric fire.

（7）Electric devices should be well insulated. When there is damage to switch, fuse case, plug or socket, replace them instantly.

（8）Repairing of electric appliances should be carried out in an OFF stage. If this is not possible, follow the ON-state procedures strictly. Before examining an electric appliance, check its electric state with a test pencil, making sure of it is zero voltage. In case electricity should suddenly be on, the main switch should be pulled off before work is started. .

（9）If a live wire falls onto the ground, never pick it up by hand. Cut off electricity first. When seeing a wire fallen on wet spot, water or mud, don’t walk toward it, in case of electric shock from pace span voltage.


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（10）The outer cover, switches and other metal bodies of every operative electric device must be connected to the grand or zero wire. When insulated cover is damaged, electricity should be shortly cut off or electric current be let into ground, so that the metal cover of electric devices have the same voltage level with the ground and incur no danger for people who might get in touch.

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