Biogas engine for minecraft 1.7 10. Main types of engines: biofuel

One of the main trends in the design of modern automotive engines is to improve their environmental performance. In this regard, one of the best options is biofuel engine, the most popular type of which is bioethanol.

Bioethanol is ethyl alcohol, which is obtained by processing plant materials. The main source for its production is starch-rich fodder crops.

Biofuel engine features

It should be noted that at the moment there is practically no talk of an engine that would run entirely on bioethanol. This is due to a number of objective limitations, for which effective solutions have not yet been found.

To date, bioteanol is used to refuel cars, mainly mixed with traditional fuels - gasoline and diesel fuel. Only vehicles with an FFV (Flexible-fuel vehicle) engine can operate on such fuel.

The FFV type motor is an internal combustion engine, which has some differences from traditional engines. So, the main distinguishing features are:

• the presence of a special oxygen sensor;
• the use of a special material for the manufacture of a number of gaskets;
• ECU software that allows you to determine the percentage of alcohol in the fuel and adjust the engine operation accordingly;
• some design changes to increase the compression ratio, which is necessary due to the higher octane rating of ethanol compared to gasoline.

Today, automotive fuel containing bioethanol is quite popular in a number of countries. The leaders here are the US and Brazil. In Brazil today, it is almost impossible to buy gasoline that contains less than 20% bioethanol. This technology is also popular in a number of European countries, especially in the Scandinavian countries.

Advantages and disadvantages

Bioethanol as a fuel has both significant advantages and significant disadvantages. The main advantages of biofuels relate primarily to environmental performance.

Bioethanol is a non-toxic fuel that dissolves completely in water. When it is burned, no compounds hazardous to the environment and human health are formed. Adding bioethanol to gasoline can reduce harmful emissions by up to 30% or more. In addition, bioethanol is produced from natural renewable raw materials. Often it is a by-product of non-waste production of other types of products.

In addition, due to the high octane number, the use of bioethanol can improve some of the characteristics of the internal combustion engine. It also increases its efficiency.

One of the main disadvantages of biofuels is their instability to low temperatures. In frost, it can delaminate with the formation of a film of paraffins on the surface. This causes difficult start-up in winter. To overcome this shortcoming, cars have to be equipped with a fuel heater or a small gas tank designed specifically for cold starts.

Another important disadvantage is the low calorific value. During the combustion of bioethanol, 37-40% less thermal energy is released compared to traditional types of automotive fuel. This significantly limits the power characteristics of the engine.

Biofuel engines have significant advantages, but they have room for improvement.

I. Trokhin

The article discusses the technical features of gas piston engines and electrical units based on them for mini-CHPs operating on natural gas or an alternative renewable gaseous fuel - biogas. When natural gas is used as a fuel, the electrical efficiency of such units reaches 48.7%, and the efficiency of the fuel combustion heat for mini-CHP is 96%.

Modern gas-piston power units, appropriate cogeneration and trigeneration technologies provide consumers with the opportunity to provide not only technically and economically profitable production of electrical, thermal energy and cold, but also to achieve this with currently acceptable environmental indicators for the emission of exhaust gases into the environment. The latter circumstance is especially positively manifested when a gas piston engine runs on biogas. The specific heat of combustion of biogas is about 23 MJ/m 3 , for comparison, natural gas - 33-35 MJ/m 3 .

The biotechnological process of obtaining biogas consists in anaerobic (without oxygen access) destruction (the terms "fermentation", "fermentation", "fermentation" are also used) of organic wastes that serve as primary raw materials ( tab. 1), resulting in the formation of a gaseous biosubstance (biogas) and high-quality organic fertilizers. The production of biogas in such a process is a very effective way of producing biofuel from biomass, and organic fertilizers are a by-product, the use of which allows to reduce the share of mineral fertilizers used in agriculture. The technical implementation of biogas production is carried out in biogas plants. To maintain their working processes, a part of the energy received from biogas at gas piston power plants is spent. Associated organic fertilizers can be stored in seasonal storage facilities. A biogas plant and a gas piston power plant (for example, a mini-CHP, i.e., with an electric power of up to 10 MW) are usually located in close proximity as a single complex for the production of biogas from organic raw materials and the subsequent generation of electrical and thermal energy

Table 1

Output of biogas and electricity from organic raw materials

Name	The volume of biogas, m 3, per ton of raw materials		Electricity generation per ton of wet raw materials, kWh
		wet
cattle
Cereal crops
potato foliage
herbal grain
biological

Note. Based on information materials from GE Jenbacher (Austria).

The composition of biogas includes the following components: methane (CH 4) as a combustible base, carbon dioxide (CO 2) and a relatively small amount of impurities accompanying biogas production (nitrogen, hydrogen, aromatic and halogen hydrocarbon compounds). Depending on the raw material base, the yield of biogas in the process of anaerobic degradation may vary. IN tab. 1 some estimates are given for this indicator, as well as for the specific generation of electricity per unit of primary organic raw materials in the "biogas plant-biogas piston power plant" system.

Directly, the technologies of cogeneration and trigeneration at gas piston power plants are based on the use of hot water waste heat boilers and absorption refrigeration units. The latter provide the possibility of useful utilization of the heat of exhaust gases from a gas piston engine, reducing their temperature when discharged into the atmosphere. In addition, the designs of modern gas piston engines allow for the possibility of beneficial use of low-grade heat from cooling and lubrication systems. Gas piston engine-electric generating units, including for cogeneration units, are developed, produced and provided with service support by many well-known companies abroad and in Russia, for example, MWM GmbH (Germany), GE Jenbacher (Austria), MTU Onsite Energy GmbH (Germany). Below are some of the design features, characteristics and implemented projects using such gas-piston power equipment.

Biogas or natural gas?

The German company MWM GmbH is one of the world's leading developers and manufacturers of gas piston systems for generating electrical and thermal energy from biogas. The constant reduction in the reserves of non-renewable hydrocarbon energy sources and the growth of energy consumption on a global scale leads to an increase in consumer demand for alternative fuels (for example, biogas) obtained from renewable energy resources, including waste. Therefore, equipment with which it is possible to efficiently produce biogas and energy does not remain without the attention of customers of decentralized energy supply installations.

MWM GmbH gas-fired generating sets, one of which is shown in rice. 1, with synchronous generators are successfully operated, in particular, in Europe, and they work, including at mini-CHPs, not only on natural gas, but also on biogas. The generated electricity can be transferred to centralized electric power systems. The implementation of the process of obtaining biogas as part of a single local generating complex is carried out on its own energy supply. For example, in Germany, a biogas reciprocating mini-CHP by Nawaro Kletkamp GmbH & Co. is successfully operating. KG (Kletkamp biogas CHP plant - English) with a TCG 2016 B V12 engine from MWM GmbH, with an electric power of 568 kW. It utilizes about 20 tons of grain silage (corn silage - English) daily, and part of the consumers of the neighboring German city of Lütjenburg (Lütjenburg - German) is provided with thermal energy. This thermal energy is also used for drying grain, and is also stored in a heat storage facility. The by-product formed in the process of anaerobic fermentation of the feedstock for biogas production is the remains of the substrate and is used as an organic fertilizer produced by this method in an annual amount of about 7 thousand tons.

Rice. 1. Gas piston engine-generator unit of MWM GmbH (Germany)

Especially for operation on biogas, parts and components of the corresponding gas piston engines from MWM GmbH are adapted and calculated. For example, the piston design is adapted to work with a higher compression ratio. To ensure high resource indicators of engine parts and assemblies, in particular, galvanic coatings are used. High energy parameters of biogas reciprocating generator sets of this company (Table 2) achieved, including by eliminating the process of pre-compression of biogas.

table 2

Nominal parameters of the MWM GmbH generating set with TCG 2016 V08 C engine for mini-CHP

Name, unit	Value when running on fuel
	(60% CH 4, 32% CO 2)	Natural
Electric power, kW
	Variable, three-phase
Voltage, V
Current frequency, Hz
Average effective pressure, bar
Thermal power, kW
electric thermal
Dry weight, kg

Note. According to the information brochures of the company MWM GmbH (Germany).

The top model range in the range of MWM GmbH gas piston engines is represented by the TCG 2016 series. These engines can operate with very high efficiency values, as can be seen from tab. 2, which is also achieved through the use of optimized designs of the camshaft, combustion chamber and spark plugs. The branded "general electronic control system" under the registered trademark TEM  (Total Electronic Management - English) ensures the coordination and operation of the entire engine-generator set. Temperature monitoring is provided for each of the cylinders. There is also a system thanks to which the engine can work effectively with fluctuations and changes in the gas composition of the air-fuel mixture. This is especially important when it is intended to use such "problematic" gases as fuel, such as coal or organic waste.

Revolutionary configuration

Innovative gas piston engines of world renown under the Jen-bacher brand ( rice. 2) is developed and produced by the Austrian company GE Jenbacher, which is part of the GE Energy division of General Electric. Decentralized power supply installations based on such engines are adapted to operate both on natural gas and other gaseous fuels, including biogas. A particularly positive economic effect from the introduction of such installations is achieved when they operate on a cogeneration or trigeneration cycle. In many developed countries, for example, Austria and Germany, gas piston power plants with Jenbacher engine-generator units in combination with biogas plants are successfully operated, in particular, with electrical and thermal capacities from about three hundred to one and a half to two thousand kilowatts.

Rice. 2. Jenbacher gas piston engine as part of an electric unit

The revolutionary, as the developers themselves call it, the three-module configuration of modern Jenbacher generating sets and the engineering concept of achieving the goal of increasing the efficiency of engines by increasing their efficiency, reliability and reducing emissions of harmful emissions into the atmosphere led to the creation of a new J920 gas piston engine with two-stage turbocharging and the highest electrical efficiency in the class of gas piston engines ( tab. 3). The three-module layout of the electric unit with this engine includes the following elements arranged in series: a module with a synchronous electric generator equipped with air cooling and a digital control system; twenty-cylinder gas-piston power module based on the J920 engine itself; auxiliary module with a two-stage turbocharged unit. Thanks to this arrangement, individual elements can be replaced without disassembling the entire generating set.

The J920 engine has a sectioned camshaft, which allows for easy replacement through an operating port located on top of the crankcase. Other basic parts and components of the engine are also easily accessible. Extensive accumulated experience in the development and practice of operating a fuel combustion system for Jenbacher type 6 gas piston engines made it possible to equip the engine in question with an advanced pre-chamber combustion system with spark ignition, which allows for long-term operation. In addition, operational monitoring of the system operation is provided using special sensors for each of the cylinders, which makes it possible to achieve optimal characteristics during fuel combustion. The ignition system is electronic, which ensures the selection of the ignition time with adaptation to the composition and (or) type of gaseous fuel used.

Table 3

Nominal parameters of a generating set with a Jenbacher J920 engine for a mini-CHP using natural gas (methane number MN > 80)

Name, unit of measurement	Meaning
Electric power, kW
	Variable, three-phase
Current frequency, Hz
Engine and generator shaft speed, rpm
Thermal power, kW
Efficiency for lower calorific value, %: electric
Overall dimensions (approximately), mm:
Dry weight (approximately), kg

Note. According to GE Energy (www.ge-energy.com).

From the exhaust manifold, part of the gases exhausted in the gas piston engine is used to drive the turbocharger (turbocharged) unit. The latter, during its operation, provides an increase in the specific power of the engine, and, consequently, in the end, the electrical efficiency of the engine-generator unit. The use of proprietary patented technology in the engine under the registered trademark LEANOX  (Lean mixture combustion - English) made it possible to implement the process of effective control of the ratio of the content of the "air / gas fuel" components in the fuel-air mixture in order to minimize the emission of harmful ecology of exhaust gases into the atmosphere. This environmental benefit is achieved by running the engine on a lean fuel mixture (the air/fuel gas ratio is adjusted below the limit of all operating values) as long as it runs stably.

Proprietary two-stage turbocharging technology makes it possible to provide the engine with a greater increase in specific power than is realized with a single-stage turbocharging. In addition, if we are talking about cogeneration plants, then with the implementation of this turbocharging technology, the overall efficiency of the electric unit also increases, reaching a value of 90%, which is almost 3% higher than that of gas-piston electric units with single-stage turbocharging.

The J920 engine management system from General Electric is comprehensively debugged and equipped, in particular, with a programmable logic unit, a control panel and information display. In addition to all this, the J920 engines are designed taking into account the permissible possibility of their operation as part of multi-engine electrical units, including at thermal power plants. The multi-engine structure of power plants makes them more adaptable to loads - from basic to cyclic and peak loads. The starting time of the engine before reaching the nominal mode is 5 minutes.

Record-breaking energy efficiency

The German company MTU Onsite Energy GmbH is also engaged in the development and production of highly efficient modern gas piston units ( rice. 3), including those intended for operation as part of a mini-CHP. It is very interesting that its specialists created a gas piston power unit of the GC 849 N5 type ( tab. 4), with the use of which in Germany at the Vauban mini-CHP (Vauban HKW) it was possible to achieve a truly record-breaking indicator for the conversion of the primary energy of combustion of fuel (natural gas) into electrical and usefully utilized thermal energy: the efficiency of the fuel combustion calorific value was about 96%! Such a high figure is ensured by the use of mini-CHP, in addition to the gas-piston unit itself, and equipment for the deep recovery of heat from exhaust gases and lubrication and cooling systems of the engine. In addition, the heat from the engine and the synchronous generator is recovered by means of an electric heat pump, which at least cools the space around the cogeneration unit. Taking into account all stages and circuits of heat recovery, at nominal operating modes for electrical and thermal loads of a mini-CHP, the noted coefficient and reaches a record value - up to 96%.

Meaning

Electric power, kW

Variable, three-phase

Voltage, V

Current frequency, Hz

The main way to use biogas is to turn it into a source of thermal, mechanical and electrical energy. However, large biogas plants can be used to create production facilities for the production of valuable chemical products for the national economy.

Biogas can be used in gas-burning devices that generate energy that is used for heating, lighting, supplying feed preparation plants, for operating water heaters, gas stoves, infrared emitters and internal combustion engines.

The simplest way is to burn biogas in gas burners, since gas can be supplied to them from gas tanks under low pressure, but it is more preferable to use biogas to produce mechanical and electrical energy. This will lead to the creation of its own energy base that provides for the operational needs of farms.

Table 18 Biogas components

Gas-burners

Fig.34. Gas stove working
on biogas in Petrovka

The basis of most household appliances in which biogas can be used is a burner. In most cases, atmospheric type burners are preferred, operating on biogas premixed with air. Gas consumption by burners is difficult to calculate in advance, so the design and adjustment of burners must be determined experimentally for each individual case.

Compared to other gases, biogas requires less air to ignite. Consequently, conventional gas appliances need wider nozzles for the passage of biogas. For complete combustion of 1 liter of biogas, about 5.7 liters of air are needed, while for butane - 30.9 liters and for propane - 23.8 liters .

Modification and adaptation of standard burners is a matter of experimentation. In relation to the most common household appliances adapted for the use of butane and propane, it can be noted that butane and propane have a calorific value almost 3 times higher than biogas and give 2 times more flame.

Converting burners to biogas always results in lower levels of appliance operation. Practical measures for burner modifications include:
an increase in jets by 2-4 times for the passage of gas;
change in the volume of air supply.

gas stoves
Before using a gas stove, the burners must be carefully adjusted to achieve:
compact, bluish flame;
the flame must spontaneously stabilize, i.e. non-burning sections of the burner should light up on their own within 2-3 seconds.

Fig.35. Water heating boiler
for home heating with radiant ceramic heaters in the village. Petrovka

Radiant heaters
Radiant heaters are used in agriculture to achieve the right temperatures for rearing young animals such as piglets and chickens in confined spaces. The required temperature for piglets starts at 30-35°C in the first week and then slowly drops to 18-23°C at 4 and 5 weeks.

As a rule, temperature control consists in raising or lowering the heater. Good ventilation is essential to prevent CO or CO2 concentrations. Therefore, the animals must be supervised at all times and the temperature checked at regular intervals. Heaters for piglets or chickens consume about 0.2 - 0.3 m3 of biogas per hour.

Thermal radiation of heaters

Fig.36. Gas pressure regulator

Photo: Vedenev A.G., PF "Fluid"

Radiant heaters implement infrared thermal radiation through a ceramic body, which is heated to a bright red state at temperatures of 900-1000°C by a flame. The heating capacity of a radiant heater is determined by multiplying the gas volume by the net calorific value, since 95% of the biogas energy is converted into heat. The output of thermal energy from small heaters is
from 1.5 to 10 kW of thermal energy8.

Fuse and air filter
Radiant heaters using biogas must always be equipped with a fuse that cuts off the gas supply in the event of a drop in temperature, i.e. when the gas is not burned.

Biogas consumption
Household gas burners consume 0.2 - 0.45 m3 of biogas per hour, and industrial ones - from 1 to 3 m3 of biogas per hour. The required amount of biogas for cooking can be determined based on the time spent cooking daily.

Table 19. Consumption of biogas for domestic needs

Biogas engines
Biogas can be used as a fuel for automobile engines, and its efficiency in this case depends on the methane content and the presence of impurities. Both carburetor and diesel engines can run on methane. However, since biogas is a high octane fuel, it is more efficient to use it in diesel engines.
To operate the engines, a large amount of biogas is required and the installation of additional devices on internal combustion engines that allow them to run on both gasoline and methane.

Fig.37. Gas power generator in the village. Petrovka

Photo: Vedenev A.G., PF "Fluid"

Gas-electric generators
Experience shows that it is economically feasible to use biogas in gas power generators, while burning 1 m3 of biogas makes it possible to generate from 1.6 to 2.3 kW of electricity. The efficiency of this use of biogas is increased by using the thermal energy generated during the cooling of the motor of the electric generator to heat the reactor of the biogas plant.

Biogas cleaning

To use biogas as a fuel for internal combustion engines, it is necessary to pre-clean the biogas from water, hydrogen sulfide and carbon dioxide.

Moisture reduction

Biogas is saturated with moisture. Purification of biogas from moisture consists in its cooling. This is achieved by passing biogas through an underground pipe to condense moisture at lower temperatures. When the gas is reheated, the moisture content in it decreases significantly. This drying of the biogas is especially useful for the dry gas meters used, as they are bound to fill with moisture over time.

Reducing the content of hydrogen sulfide

Fig.38. Hydrogen sulfide filter and absorber for separating carbon dioxide in the village. Petrovka
Photo: Vedenev A.G., PF "Fluid"
Hydrogen sulfide, mixed in biogas with water, forms an acid that causes metal corrosion. This is a serious limitation on the use of biogas in water heaters and engines.
The simplest and most economical way to remove hydrogen sulfide from biogas is dry cleaning in a special filter. As an absorber, a metal "sponge" is used, consisting of a mixture of iron oxide and wood shavings. With the help of 0.035 m3 of a metal sponge, 3.7 kg of sulfur can be extracted from biogas. If the content of hydrogen sulfide in biogas is 0.2%, then with this volume of a metal sponge, about 2500 m3 of gas can be purified from hydrogen sulfide. To regenerate the sponge, it must be held in the air for some time.
The minimum cost of materials, the ease of operation of the filter and the regeneration of the absorber make this method a reliable means of protecting the gas tank, compressors and internal combustion engines from corrosion caused by prolonged exposure to hydrogen sulfide contained in biogas. Zinc oxide is also an effective absorbent of hydrogen sulfide, and this substance has additional advantages: it also absorbs organic sulfur compounds (carbonyl, mercaptan, etc.) 18

Decrease in carbon dioxide content
Reducing carbon dioxide content is a complex and expensive process. In principle, carbon dioxide can be separated by absorption into the milk of lime, but this practice produces large volumes of lime and is not suitable for use in high volume systems. Carbon dioxide itself is a valuable product that can be used in various industries.

Fig.39. UAZ powered by biogas
in with. Petrovka
Photo: Vedenev A.G., PF "Fluid"

Methane use
Modern research by chemists opens up great opportunities for the use of gas - methane, for the production of soot (dye and raw material for the rubber industry), acetylene, formaldehyde, methyl and ethyl alcohol, methylene, chloroform, benzene and other valuable chemical products on the basis of large biogas plants18.

Biogas consumption by engines
In with. In Petrovka, Chui region of the Kyrgyz Republic, the biogas plant of the Association "Farmer" with a volume of 150 m3 provides biogas for domestic needs of 7 peasant farms, the operation of a gas-electric generator and 2 cars - UAZ and ZIL. To operate on biogas, the engines were equipped with special devices, and the vehicles were equipped with steel cylinders for gas injection.
The average values ​​of biogas consumption for the production of 1 kW of electricity by the engines of the Farmer Association are about 0.6 m3 per hour.

Table 20. Use of biogas as motor fuel in the village Petrovka

Fig.40. Flare burner for burning excess biogas in the village. Petrovka
Photo: Vedenev A.G., PF "Fluid"

Biogas efficiency
Biogas efficiency is 55% for gas stoves, 24% for internal combustion engines. The most efficient way to use biogas is as a combination of heat and power, where 88% efficiency can be achieved8. The use of biogas for the operation of gas burners in gas stoves, heating boilers, fodder steamers and greenhouses is the best use of biogas for farms in Kyrgyzstan.

Surplus biogas
In case of excess biogas produced by the plant, it is recommended not to release it into the atmosphere - this will lead to an adverse effect on the climate, but to burn it. To do this, a flare device is installed in the gas distribution system, which must be located at a safe distance from the buildings.

Experience in the operation of gas piston units on biogas

1. Introduction

The task of modern energy is to provide a reliable and long-term energy supply while conserving fossil fuel resources and protecting the environment. This requires an economical approach to the use of existing energy resources and the transition to renewable sources. A study by the European Commission has shown that this is possible.

When conducting the study, only the technologies available on the market today were taken into account, and it was assumed that the standard of living in European countries would be equalized. Thus, by 2050, 90% of the energy consumed by European countries may well be produced using renewable energy resources (Fig. 1). At the same time, the price of electricity will double, but at the same time, energy consumption will also be halved. Almost a third of energy will be produced from biomass.

Figure 1 - Energy consumption in Europe (European Commission study)

Biomass is a general term for organic products and waste (slurry, grain residues, oil and sugar crops), industrial and domestic waste, wood, food industry waste, etc. Dry biomass can be immediately used as fuel, in other cases it can be converted to biogas by "digestion", gasification or evaporation (Figure 2).

Figure 2 - Use of biomass

2. Formation of biogas

In nature, biogas is formed by the decomposition of organic compounds under anaerobic conditions, such as in swamps, on the banks of water bodies and in the digestive tract of some animals. Thus, the physics of natural processes shows us the ways to obtain biogas.

Industrial production requires the development of an integrated technology that includes components such as a biomass storage tank, a biogas reactor (fermenter) in which digestion takes place, and a biogas tank with a cleaning system (Fig. 3).

Figure 3 - Production of electrical energy using biogas

Almost all organic matter is decomposed by fermentation. Under anaerobic conditions, the microorganisms involved in the process of fermentation or decomposition adapt to the original substrate. Due to the fact that fermentation occurs in a humid environment, the biosubstrate should contain approximately 50% water. Biological decomposition is carried out at a temperature of 35 °C to 40 °C. During anaerobic fermentation, a multi-stage process of converting organic substances from high molecular weight compounds to low molecular weight compounds that can be dissolved in water takes place. At one stage, the dissolved substances decompose, forming organic acids, low-grade alcohol, hydrogen, ammonia, hydrogen sulfide and carbon dioxide. On the other, bacteria convert substances into acetic and formic acids and, in the process of methanogenesis, break them down, forming methane.

4 HCOO H → CH 4 + 3 CO 2 + 2 H 2 O

At the same time, the CO 2 content is reduced by hydrogen, as a result of which methane is also formed.

CO 2 + 4 H 2 → CH 4 + 2 H 2 O

Liquid manure is often used as a feedstock for biogas production. To increase the gas yield, so-called coenzymes can be added, which homogenize the production of biogas, the volume of which depends on the substrate used (Table 1).

Table 1 - Biogas yield for different types of biomass

Raw materials for biogas	Biomass quantity	Biogas quantity
Liquid manure (cattle)	1 m 3	20 m 3
Liquid manure (pigs)	1 m 3	30 m 3
bird droppings	1 m 3	40 m 3
sewage sludge	1 m 3	5 m 3
Biowaste	1 ton	100 m 3
Waste fats	1 ton	650 m3
Grass	1 ton	125 m 3

3. Quality of biogas and its preparation for use

The quality of biogas and the preparation of fuel gas does not depend on the feedstock used and on the speed of the process. In Table. 2 shows a comparison of the composition of different types of gas.

Table 2 - Approximate comparative composition of fuel gases

		Biogas	Gas Wastewater	Garbage gas landfills	Natural gas
CH 4	%	50...75	65	50	88
CO2	%	20...50	35	27	—
N 2	%	0...5	—	23	5
Density	kg/nm 3	1,2	1,158	1,274	0,798
Calorific value ability	kWh/Nm 3	5,0...7,5	6,5	4,8	10,1
methane number	units	124...150	134	136	80...90

Since biogas contains such harmful components as sulfur, ammonia, sometimes silicon, as well as their compounds, the possibilities of its use are limited. These components can cause wear and corrosion of internal combustion engines, so their content in the gas should not exceed established MWM norms. In addition, the exhaust gases must not be cooled to temperatures below 140...150 °C, otherwise acid condensate will accumulate in the heat exchangers and in the lower part of the exhaust gas duct system.

There are several ways to remove sulfur from fuel gas. During biological treatment, air is supplied to the gas zone in the fermenter. As a result of hydrogen sulfide oxidation by bacteria, sulfur and sulfate are separated, which are removed with liquid components. Another way is chemical precipitation. In this case, iron trichloride is added to the solution in the fermenter. These methods have proven themselves well in wastewater treatment plants.

The most optimal results are achieved when gas is cleaned using activated carbon, and not only sulfur, but also silicon is removed from the gas. In this case, the quality of the biogas matches the quality of natural gas, and the use of an oxidizing catalytic gas neutralizer provides an additional reduction in exhaust gas emissions.

4. Use of biogas for CHP based on gas piston engines

MWM GmbH (formerly Deutz Power Systems) manufactures lean-burn turbocharged gas piston units in the rated power range from 400 to 4300 kW (Fig. 4). These engines are adapted to fluctuations in the composition of biogas and are optimized for operation on gases with complex compositions.

Figure 4 - Power range of gas engines MWM GmbH (former DEUTZ Power Systems)

Ratings are in accordance with ISO 3046. Specifications are for information only and are not binding values.

MWM GmbH has extensive experience in operating gas piston engines on landfill and sewage gas (the first such models began to operate almost 100 years ago on sewage gas) and uses this experience to further improve the model range and increase the reliability of manufactured cogeneration systems. (Fig. 5)

Figure 5 - Development of gas piston engines (for the period 1988 - 2002)

The main task in this case is to make the engines more resistant to the effects of harmful substances contained in the gas. Various impurities form acids that adversely affect engine components, primarily bearings. Such a negative impact can be eliminated, on the one hand, by optimizing the operating mode and changes in bearing manufacturing technology, on the other.

If the unit is operated with a lubricating oil temperature of around 95°C (engine inlet) and frequent stops and starts are avoided, the risk of acid formation due to condensation in the crankcase during the cooling phase can be reduced. In connection with the above, as far as possible, the engine should run without stopping. Accumulation of gas in sufficient volume in the gas storage will provide a continuous supply of fuel, which is necessary for the smooth operation of the gas engine.

Experience gained in the operation of biogas engines has shown that special materials must be used for bearings. As motor efficiency and operating pressure increase, bearings with higher load ratings are needed. Coated bearings are now widely used to meet all reliability requirements. Thanks to their continuous hard surface, they are more resistant to aggressive gas and lubricating oil than traditional grooved ball bearings (fig. 6).

Figure 5 — Peak film pressure comparison

Lubricating oil quality has a significant impact on engine life and wear. Therefore, during operation, only those brands of oil that the gas engine manufacturer has approved for this type of gas should be used. Oil change intervals are determined when the power plant is commissioned based on the results of an oil quality analysis. During the operation of the engine, the quality of the lubricating oil is constantly monitored, after which a decision is made to replace it. The first oil analysis is performed after 100 hours of operation, regardless of the type of fuel gas. The maintenance intervals for valves are determined in the same way.

In order to extend the lube oil change intervals, the amount of oil in the base frame of the engines must be increased. For this purpose, MWM offers its customers units with increased oil volume in the engine frame. Oil is constantly supplied to the lubrication circuit, passing diagonally through the base frame (Fig. 10):

Figure 6 - Lubricating oil supply

In addition to the design features of the motors themselves, the control and management system TEM (Total Electronic Management by MWM) plays an important role in ensuring the safe and reliable operation of biogas units. It detects all operating conditions, temperatures, pressures, etc. and, based on the data obtained, sets the optimum engine power output at maximum efficiency, while not exceeding the established emission limits. The TEM system has the option of drawing up analytical graphs of changes in the operating parameters of the station - this allows you to timely detect violations in the work and quickly respond to them.

The company supplies complete power plants running on biogas. They include a gas piston unit, a waste heat boiler, a silencer, catalytic gas converters, an activated carbon gas cleaning system and, if required, an additional exhaust gas aftertreatment system. (Fig. 7).

Figure 7 - An example of the layout of a mini CHP ( click on image to enlarge)

On fig. 8 shows the specific investment and average maintenance costs for biogas plants. The data summarizes the operating experience of the TBG 616 and TBG 620 series units. It includes the costs of the gas engine, coolant and exhaust gas heat exchangers, silencers, and the costs of the distribution plant, including installation and piping. Since 2005, the TBG series units have been upgraded to the TCG 2016 C and TCG 2020 series, respectively.

Figure 8 - Capital investment and maintenance costs

In 2009, after the next modernization of the model range, for the TCG 2020 series, it was possible to achieve an electrical efficiency equal to 43.7% for the TCG 2020 V20 cogeneration unit, and to bring the electrical power of 12 and 16-cylinder gas engines, respectively, to 1200 and 1560 kW. Serious modernization also affected the TCG 2016 V08 unit. The electrical power of this unit has been increased to 400 kW, and the electrical efficiency has increased to 42.2%. Moreover, the electrical efficiency and output power are the same both when using natural gas and biogas.

5. Practical use of various raw materials for energy generation

In the city Brandenburg(Germany) installed a power plant that produces biogas from food and household waste (photo 1). Approximately 86,000 tons of biowaste are disposed of annually.

Photo 1 - Biogas plant in Alteno

The process of obtaining biogas is carried out in a certain sequence. After the non-disposable components are removed, the biowaste is crushed and mixed, the resulting mass is heated to 70 ° C to kill pathogenic organisms. The waste is then sent to two fermenters, each holding 3,300 m3 of biomass. Microorganisms break down the biomass (in about 20 days), resulting in the formation of biogas and a residual amount of liquid, which is then squeezed out, and the dry residue is again biologically processed as compost.

Two gas piston engines TBG 616 V16K manufactured by Deutz Power Systems operate on biogas, the electric power of each of them is 626 kW, the thermal power is 834 kW. The generated electrical energy is fed into the power grid, and the heat is used to generate gas. Emission levels of harmful substances are below the limit values ​​specified by the German TA-Luft standard.

The biogas plant also operates in Eichigte at the livestock farm of Agrofarm 2000 GmbH. The company cultivates 2,200 hectares of arable land and 1,100 hectares of pasture in Eichigt/Vogtland. Part of the harvest of cultivated crops is used as feed for 1550 cows, from which 10,650,000 kg of milk are produced per year. At the same time, from 110 to 120 m 3 of liquid manure is formed daily - it is “fermented” in the fermenter, as a result of which 4000 ... 4400 m 3 of biogas is produced. Feed residues (up to 4 t/day) are added to manure, due to which gas production is increased by 20%.

The mini-CHP is installed in a container (photo 2), a TBG 616 V16 K engine is used as a drive, the electric power of which is 459 kW, the thermal power is 225 kW. Electricity is supplied to the power grid, and heat is used for the needs of the economy. Liquid manure is used as raw material for biogas.

Photo 2 - MWM cogeneration unit (former DEUTZ Power Systems) in container version with TBG 616 V16 engine

The biomass recycling cycle is practically waste-free. The residues generated from the anaerobic "digestion" process are odorless and can be used in the fields as fertilizer throughout the year.

conclusions

• The use of agricultural waste as biofuel allows for a closed cycle of agricultural production. The residue from anaerobic digestion is odorless and can be taken to the fields as fertilizer. This type of fertilizer is immediately absorbed by plants without polluting the soil or groundwater.
• The generation of energy from biogas, in the light of regular energy crises, is considered a promising renewable energy source. Biogas plants convert solar energy stored by plants into biogas through a biodegradation process. This process is neutral in terms of CO 2 balance, since only the amount of carbon dioxide that was previously absorbed by plants during photosynthesis is released into the atmosphere.
• The generation of electrical and thermal energy in biogas plants is a promising technology that helps humanity become independent from the limited reserves of fossil fuels, and also protects the environment.
• MWM GmbH offers its customers power and heat generation systems based on modern, safe and reliable gas engines.

The original article was printed for: VIth International Scientific Conference GAS ENGINES 2003 in Poland, 02 - 06 June 2003