REPORT REDUBAR WP02 D02 EIE/06/221/SI

Transcription

1 REPORT Work package: WP02 Technological and non-technological evaluation of heating, cooling and power generation from biogas Start data of the action: 1 st of December 2006 End data of the action: 31 st of May 2009 Deliverable: D02 An evaluation- and datasheet Economical, energetically and ecological efficiency of the combined power, heat and cold generation from biogas in on-site supply chains for all participating countries. Month of completion: 25 (December 2008) Responsible partner: DBI Gas- und Umwelttechnik GmbH redubar@dbi-gut.de and Energy Agency of Vysocina (EAV) Date: 19 December 2008 REDUBAR WP02 D02

2 Contents Contents... 2 Abstract Introduction Combined production of electricity and heat in biogas plants Technology for cogeneration production of heat and electricity Technical and ecological boundary conditions of refrigeration Trigeneration Technological solution Comparison of economic parameters of heat and mechanical driven refrigerating processes Comparison of energetic parameters and CO 2 -emission of heat and mechanical driven refrigeration systems as well Examples and calculations Conclusion...34 Literature

3 Abstract Cogeneration is one of today s most environmental and at the same time economically feasible ways of generating electricity and heat. Efficiency of the cogeneration units is between 80 90%. In addition, in case of smaller decentralized sources the electricity and heat are produced and consumed in the same place, which eliminates the distribution expenses and losses caused by the distribution. The electricity produced in the decentralized cogeneration source is used to cover the power consumption of the building it is situated in and the excess can be sold to network. Problems have to be solved when burning biogas off-site, in the place of consumption: Supplying the biogas plant with heat and electricity for self-consumption. Treatment and transport of gas Building the engine room for the cogeneration units off-site Securing consumption of electricity and heat during the whole year In the text we will compare the advantages and disadvantages of on-site (in the place of production) and off-site (in the place of consumption) biogas utilization. On site: Lower investment Lower revenues (no revenues for heat) Simple accounting Lower operation costs Off-site: Higher investment Higher complexity of inner relations Gas treatment costs Costs of self-consumption heat and electricity source Costs of decreasing self-consumption of heat Economical efficiency off-site will be much higher, mainly due to greater revenues for selling heat and cooling. Operating cogeneration sources on the place of consumption brings: Significant reduction of emissions, mainly of CO 2 Better economic parameters, project is realizable More than twice as high energy efficiency 3

4 It can be assumed, that even better results could be achieved, but only in some of the categories. E.g. by using ORC we increase the environmental and energy efficiency, but make worse the economic parameters significantly. Using of each technology has to be evaluated carefully regarding the conditions of each particular project and a detailed feasibility study has to be created. 4

5 1. Introduction About cogeneration Cogeneration is one of today s most environmental and at the same time economically feasible ways of generating electricity and heat. Efficiency of the cogeneration units is between 80 90%. In addition, in case of smaller decentralized sources the electricity and heat are produced and consumed in the same place, which eliminates the distribution expenses and losses caused by the distribution. The electricity produced in the decentralized cogeneration source is used to cover the power consumption of the building it is situated in and the excess can be sold to network. The heat produced in the cogeneration unit is used for heating the buildings, for hot supply water, or for preparation of technological heat. Cogeneration units are also used as an emergency electricity sources in places of constant consumption. It is possible to use the heat in an absorption exchanger to produce cooling for technological purposes or air-conditioning. In that case we speak of trigeneration, combined production of electricity, heat and cooling. It holds generally, that it is good to use cogeneration if it is economically feasible. It is possible to use cogeneration units in all buildings with demand for electricity and heat (or cooling). They are particularly health services, schools, swimming pools and spas, dumps and agricultural production units. Considering the increasing prices of fossil fuels, the energy saving is necessary. It is said in the new IEA (International Energy Agency) abstract, that current global trends in energy supply and consumption are untenable in the long-term in economical, social and environmental terms. The absolute utilization of energy and savings can be achieved by cogeneration (or trigeneration) units (producing heat and electricity, or heat, electricity and cooling). Earth gas and biogas cogeneration has the greatest development potential and legislative support. IEA issued a report in November about the need to transform the world energetics towards greater tenability. According to IEA, if this is not done, there is a threat of a disaster in future. Currently, in power plants 30% of energy in fuels is transformed to energy and 70% is lost, let out. Cogeneration is the most effective way of using heat energy in one technological chain. That means that the building has one source of energy from which it is heated (or cooled in summer), producing electricity at the same time. Cogeneration is based on combustion engines or turbines powered by natural gas, which produce electricity and heat. They have better efficiency than common energy sources because of that. The types of industry, for which cogeneration is useful are for example paper, wood-working and food industry. In the time of increasing energy costs, the so-called mini cogeneration is a lucrative solution for private properties. Natural gas mini cogeneration is comfortable, economical and environment friendly type of energy supply for the owner of the building. The absorption exchanger can be used to produce cooling for technological use or air-conditioning from heat. In that case we speak of trigeneration, combined production of electricity, heat and cooling. According to the G8 countries the worldwide greenhouse gas emissions should drop to 50% in European association COGEN EUROPE, founded in 1993, works on reducing the greenhouse gas emissions by the development of cogeneration. By burning methane in the form of biogas much less carbon dioxide is evolved and other usual emissions are minimal or zero. Moreover, it is highly effective fuel utilization. It is a technology, which has future. The IEA study states clearly, that current global trends in energy supply and consumption are untenable in the long-term. The European Commission also recommends to the member countries to support cogeneration. 5

6 Cogeneration principles Cogeneration means combined production of electricity and heat. Compared to classic power plants, in which the heat is let out to the atmosphere, a cogeneration unit uses heat for heating and thus saves fuel and costs for its purchase. Biogas is burned in a cogeneration unit a combustion engine optimized for burning biogas. At the same time, the quality and performance is being evaluated according to the content of methane in biogas (the more methane the better). Burning biogas creates a waste heat, which is used for heating, drying wood or agricultural crops. The heat can be used in surrounding buildings or for cooling. If the heat is used properly, the economics of the biogas plant can be much better. When using the waste heat, the payback period is c. 6 years. How cogeneration unit works In a cogeneration unit the electricity is produced in a similar way as in other power plants by an electric generator, in this case powered by a combustion engine. These engines are constructed and optimized for burning biogas, but can also burn other liquid or gas fuels. Heat produced by the engine (collected by means of cooling of the engine, oil and burnt gases) is effectively utilized, thus making the efficiency of cogeneration units 80 90%. Cogeneration and trigeneration Cogeneration is one of the most important alternative energy sources. The term cogeneration is often used in a narrower sense meaning combined production of electricity and heat. The technical implementation is called cogeneration unit. The advantage is saving 40% of the primary fuel for the same amount of electricity and heat produced. This is accompanied also by reduction of emissions. The cogeneration units use various principles: Steam or combustion turbine (usually industrial heat stations or large municipal heat systems) Cylinder combustion engine New technologies and trends (e.g. micro turbines, Stirling engine, fuel cells) The most common application is the piston combustion engine, in terms of power range and project flexibility. Primary fuel is in most cases natural gas or biogas. Piston combustion engines are used not only as primary sources of electricity and heat, but also as emergency sources (e.g. hospitals) or for increasing of electrical input of a property (solves problems of lack of capacity by electrical company on site, no need for new high-voltage supply and substation). New trend is to use cogeneration units for producing electricity, heat and cooling so called trigeneration. In this case, cooling is used for air-conditioning of commercial properties, warehouses, department stores etc. Implementing is also supported by regional gas companies (reduction in price). New opportunities for mass utilization of cogeneration units arise in connection with the construction of biogas plants in agriculture, industry and waste disposal. In this case the cogeneration units secure the energetically utilization of the produced biogas. 6

7 2. Combined production of electricity and heat in biogas plants The technology of biogas production is known for decades. It is based on the process of anaerobic fermentation the organic matter is decomposed in an anaerobic environment containing microorganisms. Biogas is evolved, which can be used further for burning in cogeneration units. Biogas is a colorless gas containing mainly methane (CH 4 ) and carbon dioxide (CO 2 ). The byproduct of the anaerobic fermentation is a digestate, remnants of the original input material, which can be used as a quality fertilizer for agricultural purposes or a composting stage may be employed. The electricity produced can be used on site or supplied to distribution network. Sludge from sewerage plants can be used for producing biogas, as well as agricultural products (vegetable/animal production) and other biodegradable waste, including such waste that is hard to process in other way. The biogas plant cannot be a source of bad smell to its surroundings. This applies not only for the building itself, but also for the digestates used for fertilizing outside. The parameters and technological setup of the plant must be conformed to this primary requirement. The parameters of biogas Biogas (BG) is a mixture of gases, mainly of methane (CH 4 ) and carbon dioxide (CO 2 ). It evolves by anaerobic fermentation (digestion). Energetically usable BG is produced in specialized facilities biogas plants (BGP). BG is also produced in municipal waste dumps, where it can be collected by a system of wells and pumping stations. The main heating component of BG is methane. It can contain some undesirable compounds depending on the origin (type of biomass used). These compounds have impact on lifetime of some technological units. Due to air protection legislation, emission limits of sulphur compounds must be considered. Some BGPs are equipped with desulphurization systems. 3. Technology for cogeneration production of heat and electricity The combined production of heat and electricity can be achieved by three different technological processes. Each has different conversion level of the primary fuel. Gas cogeneration is production of electricity and heat by a direct burning in a combustion engine (Otto cycle) or in a combustion turbine (Brayton cycle), which powers an alternator, using the waste heat at the same time. The level of conversion from the energy contained in the primary fuel to the electricity is ca %, heat production efficiency is ca %. Total efficiency is thus 72 88%. Cogeneration units with combustion engine Cogeneration unit with combustion engine consists of a spark ignition combustion engine powering an alternator, which generates electricity, and exchangers for utilization of waste heat. The Otto cycle describes the process thermodynamically. A mixture of natural gas and combustion air is taken in under pressure generated by a turbo compressor power by burnt gas. That means, that the cogeneration unit doesn t need a pressurized gas input, it can be gas from standard piping with reduced pressure (tens of kpa). 7

8 The waste heat from the engine is taken away by two exchangers, each on different temperature level. The first one takes out the heat from the engine block and oil (ca C). The second one takes out the heat from the burnt gas ( C). The exchangers are series-connected by the heat-carrying medium. The cogeneration units are usually projected to supply heat to a warm-water system at 90 / 70 C, less common is 110 / 85 C. The return water from a warm-water system (70 C) passes through first exchanger, where it is pre-heated, and then through second exchanger, getting the required temperature (90 C). Rarely is the heat transmitted by hot water (from engine block) and steam (from burnt gas). To be able to temporarily run without heat output (or with limited heat output) the units are usually equipped with emergency cooler, which lets the heat into the atmosphere. Electrical efficiency (ratio of el. output of the alternator and gas input) is ca % for cogeneration units. Electrical efficiency increases with increasing compression ratio and with increasing surplus of combustion air. Electrical efficiency is given for nominal output of a unit, decreasing the output doesn t change the electrical efficiency significantly (unlike the units with combustion turbines described later). Heat efficiency of the units (ratio of usable heat output and gas input) is ca %. That means that total efficiency is ca %. Cogeneration units with spark ignition combustion engine are installed with electrical output range of ca. 20kW to 5000kW. There are emission limits for combustion engine cogeneration units burning natural gas regarding the reference content of oxygen in burnt gas 5%: NO x 500 mg/nm 3 CO 650 mg/nm 3 Usual content for combustion engines in operation: NO x ca mg/nm 3 (when free-way catalyst is used 100 mg/nm 3 ) CO 650 mg/nm 3 (when oxidizing catalyst is used 30 mg/nm 3 ) Cogeneration units with combustion micro turbines The efforts to use combustion turbines also in small cogeneration sources (> 1MW) has lead to development of so-called gas micro turbines recently. These small sources have capacity from 30 kw and thus can be used in other sectors, not just industry. These small, powerful and low-emission gas turbines can supply electricity to dwelling houses, administrative buildings, hotels, shopping centers, airports, sports centers, water works, sewerage works, schools, hospitals, small central heating supply systems, small businesses. Being compact and highly reliable, the micro turbines are suitable for combined heat and electricity production. The economic efficiency can be observed when in use more than 5000 hours per year. That is mostly the case of big hotels, shopping centers, sports centers, international airports, sewerage works, block boiler houses and hospitals. The technology is based on aircraft engine turbines and it is also often made by aircraft producers. The micro turbines can usually use gas or liquid fuel. There are also test turbines powered by gas made of biomass in operation. Currently, there are compact sets of gas turbine and electric generator available, which are combined with burnt gas boiler and sold on market as compact ready-to-use units. They are available with electric output of 35 to ca. 200kW. 8

9 Table 1: Simple comparison of 3 sources based on progressive technologies Output 100 kw Piston engine Efficiency Electricity % Heat % Total % Temperature and output medium 40 (35) 50 (55) C hot water, steam Output Heat/Electricity Fuel consumption for separate production 1,25 (1,57) 2 (1,65) Fuel Cell C hot water 0,78 1,97 Micro turbine C steam 1,66 1,67 Energy utilization of biogas It is possible to use biogas in the same way as other gas fuels. The most common implementations are: Direct combustion (heating, drying, cooling, warm water etc.) Production of electricity and heating of heat-carrying medium (cogeneration) Production of electricity, heating of heat-carrying medium and production of cooling (trigeneration) Powering combustion engines or turbines to get mechanical energy Use in fuel cells Most common use of biogas are the cogeneration units. This method has high efficiency of conversion of energy from biogas to electricity and heat (90 90%). Roughly 30% of the biogas energy is transformed to electricity, 60% to heat energy and the rest are heat losses. 0,6 0,7m3 of biogas with 60% CH4 has to be burned in the cogeneration unit to obtain 1kWh. So for production of 1kWhel and 1,27kWhth is needed 5-7kg of biomass waste, 5-15kg of communal waste or 4-7m3 of liquid communal waste. Steam gas cogeneration By combining of combustion and steam engine (so called steam gas cycle), taking advantage of it s specific energy properties, it is possible to achieve a higher level of conversion from chemical energy of the fuel to electricity, than by a cogeneration unit with only combustion engine. So by steam gas cycle we mean a combination of a combustion turbine (or, rarely, combustion engine) with a steam counterpressure steam machine unit. By this combination we eliminate the disadvantages of both technologies high temperature of burnt gas of a combustion turbine and relatively low input temperature of a steam circle. The steam made in the boiler by the burnt gas heat from the combustion engine powers a steam turbine. A higher steam parameter is needed, but the boiler cannot be too large and expensive, so there has to be a corresponding heat drop between the steam and burnt gas. This requires increasing the temperature of burnt gas in the boiler in some cases the gas is reheated by a burner. 9

10 The ratio of fuel supply to the turbine and to the burnt gas boiler determines the ratio of output of the combustion turbine and steam turbine. Bigger implementations usually use a burnt gas boiler with two pressures and corresponding two pressures steam turbine. The ratio of output of combustion and steam turbine is ca. 3:1 to 4:1 in most cases. The steam gas cogeneration can be also based on Cheng cycle: The steam made in burnt gas boiler is led to combustion chamber of the combustion turbine, which increases the weight flow on the vane. Thus is increased not only output of the combustion turbine (in this mode partially working partly as a steam turbine) but also the efficiency of the turbine. The steam supplied to the combustion chamber does not have to be overheated, which has positive effects simplicity and lower price of the burnt gas boiler and also better cooling of burnt gas coming out of the boiler. The consequence is increased efficiency of the steam gas unit. On the other hand there are disadvantages higher operation costs for constant supply of specially prepared water. Ratio of the injected steam solids to burnt gas is between 3 and 20%. Implementing the Cheng cycle increases the turbine output by up to 40% and it s efficiency by up to 8%. Steam gas cogeneration is implemented usually in higher output units (ca. > 5MW) due to it s complexity. Because it is possible to change the ratio of amount of steam brought to the turbine (or injected to combustion chamber) and the amount of heat brought to consumption, it is possible to operate the steam gas cogeneration unit (classic, with steam turbine, or Cheng cycle type) in wide range of ratios of electrical and heat output, according to consumption needs. One of the future trends may be a steam gas cycle using the ORC (Organic Rankine Cycle) technology. ORC is a power plant type condensation cycle using a mixture of organic compounds (e.g. silicon oil, it must have suitable thermodynamic properties) in the primary circuit instead of water. The advantage of oil is that it can be liquid at given temperature (e.g. 300 C) with much less pressure than water. In the evaporator the oil transmits the heat to the second circuit, where the organic matter evaporates gaining greater pressure than the oil. The organic fumes are lead to the steam turbine, where they expand. The steam is lead to the condenser behind the turbine, it condensates after giving it s heat to cooling water, which then supplies the connected objects with heat. The organic compounds used in the primary circuit have to comply with regulations and norms regarding the environment. The typical implementation of ORC is in the biomass boiler houses, where the primary energy in biomass is used both for producing heat and electricity. In this case the total efficiency ca. 85%. For comparison, a classic power plant has total efficiency of ca. 30%, letting the heat into the atmosphere. The steam generator is replaced by oil boiler and an evaporator. Oil heated in the boiler is used as a heat carrying medium, which supplies the heat through the evaporator to the second circuit. The saturated steam of organic compounds is brought to the axial turbine, which is directly connected with the generator. The heat from the condenser, which liquidizes the steam, is used (cogeneration) e.g. in small central heating supply systems. Another use is for drying wood in wood processing facilities. Arrangement scheme of the ORC cycle used for biomass cogeneration The ORC filling is loaded by a pump from condenser through regenerator back to evaporator. The burnt gas from oil furnace is used for preheating the oil filling itself, for preheating the combustion air for the oil boiler and for heating the heating water to the required temperature 10

11 Figure 1: Scheme of the ORC cycle 1 Saturated steam of the working fluid 1-2 Expansion in the turbine 2 Overheated steam 2-3 Cooling of the organic compound steam to the point of saturation (inner recuperation) 3-4 Condensation of the steam 4-5 The working fluid is transported by a pump 5-6 heating of the working fluid in recuperator 6-1 heating of the working fluid in evaporator T01 Temperature of the oil on the point of input of the evaporator T02 Temperature of the oil on the point of output of the evaporator W1 Temperature of the water entering the condenser (the returning water) W2 temperature of the water coming out of the condenser (supply water) Advantages in comparison with classic steam cycles: Direct connection of the generator without gear box due to lower speed of the turbine Minimal erosion of the turbine vanes (no droplets of the working fluid) Sources of heat with low temperature can be used Lower temperature and pressure in whole circuit Higher lifetime Not demanding to operate No need to refill and treat the water (losses are minimal) Relatively high efficiency on lower temperature drops Lower operational costs Currently, the ORC systems are supplied mostly as standardized modules with electric output of hundreds of kwel to several MWel for implementation in systems for combined production of electricity and heat from biomass, geothermal energy sources, solar systems and waste heat systems. 11

12 Measurable investment costs for the cogeneration equipment with output of 100 to kwel related to installed electric output are in these ranges: System with counter pressure turbine: ca Euro/MWel Cogeneration units with combustion engines: ca Euro/MWel Cogeneration units with combustion turbines: ca Euro/MWel Steam gas cogeneration units: ca Euro/MWel It holds generally, that the investment costs are proportional to the output. By the ratio of electric and heat efficiency of a specific cogeneration unit is given also the ratio of it s nominal electric and heat output (kwel : kwth, MWel : MWth). Table 2: Ratios of electric and heat ouput Type of cogeneration unit Ratio of electric and heat output Counter pressure steam turbine 1:6 to 1:9 Combustion engine 1:1 to 1:1,6 Combustion turbine 1:1,7 to 1:2,1 Steam gas 1:1,2 to 1:2,1 It is possible to implement cogeneration units with combustion engine only in those cases, when the produced heat can be used in the form of warm (90/70 C) or hot water (110/85 C). In many industrial plants the heat demand is limited to steam supply, so only cogeneration unit with combustion turbine or steam gas unit can be implemented. To achieve economically feasible operation of the cogeneration unit it has to be operated to 1. Maximize the use of produced heat (not only electricity) 2. Increase the value of not only the heat, but primarily of the electricity produced 3. Run most time of the year. To fulfill these three conditions the output of the unit has to be suitably adapted to daily and yearly heat and electricity consumption of the object in question. In the case of larger industrial plants and larger communal objects (hotels, shopping centers, hospitals) the output is of the cogeneration unit is optimized primarily to cover electricity consumption and then is checked the heat utilization level. In the case of community boiler houses a small part of energy produced covers the self consumption and the rest is supplied to the local network (usually not limited), so the output is primarily optimized according to the supply needed by the network. To fulfill the condition to maximize the use of produced heat the installed output has to be optimized according to daily and yearly course of heat consumption and according to the type of the unit (ratio of electrical and heat output). 12

13 4. Technical and ecological boundary conditions of refrigeration To produce cold means to remove heat away from a defined room, to create or hold a temperature which is lower than the ambient temperature. This technical process requires expense of energy. The refrigeration cycle is the reverse of a heat engine (Figure 2). See Figure 3. Figure 2: ideal cycle of a heat engine Figure 3: ideal cycle of refrigeration Figure 3 shows an ideal refrigeration cycle. The refrigerant evaporates by heat absorption a temperature T 0 below the ambient temperature TU. The vapour is compressed by supply of mechanical energy. Afterwards the vapour condenses by heat output to the ambience. The use of a refrigerating process exists in the specific cooling energy q 0. The energy w is the expense. The quotient of both terms is the efficiency of refrigeration ε C, also called coefficient of performance COP. The ratio of a real coefficient of performance to an ideal one is described with the standard ν = ε / ε C. Values between 0.4<ν<0.6 can be found for multitude of refrigerating systems. 13

14 Figure 4: COP of refrigerating processes as function of refrigerating temperature t 0. Curve 1: theoretical COP, Curve 2: COP of a real refrigerating process with a standard of ν = 0.5. The energy demand becomes higher with falling refrigeration temperature T 0. Figure 5: Theoretical COP of refrigeration. The curve determines for an ambient temperature of 32 C. The marked point is true for a temperature of 6 C (standard case for air conditioning). The real COP ranges between 3 and 6 at the standard temperatures of air conditioning. The operation with 6 C is quite common, although higher use temperatures would be sufficient 1 for many applications of refrigeration. In practice, cold is often made of a temperature level which is not really needed. 1 The real task of an air conditioning system is to realize a room temperature in a comfortable range (20 C 26 C). 14

15 The COP of the electric driven refrigerating process is the ratio of cooling capacity and electrical power. The electric power P elt itself is transformed from fuel in a power station with a specific efficiency η elt,kw. Therefore the COP can be defined relating to the primary energy demand for electric driven refrigerating processes also. 4.1 Heat driven refrigerating processes Every heat driven refrigerating process links a right-running with a left-running cycle. For the energetic rating a coefficient of heating is used. To compare mechanic driven refrigeration with thermal driven refrigeration it is necessary to calculate the ratio of cooling energy and primary energy input. Both, the coefficient of heating of the sorption process as well as the coefficient of performance of a compression process will be called COP. This is allowable only if the refrigerating energy refers to the primary energy W Br. The comparison of primary energetic efficiency shows, that compression processes outclasses sorption processes. The heating temperatures of heat driven processes are limited to max. 180 C caused by procedural reasons. The lower the heating temperature, the worse is the efficiency. 4.2 Procedures of heat driven refrigeration Heat driven refrigerating systems work with two different principles absorption or adsorption principle. Absorption means to take up (to absorb) refrigerant vapour in a solution. Adsorption means to attach refrigerant vapour at a compact material. 15

16 Absorption refrigeration machine (AKA): Two pairs of working fluids are common. One is water as refrigerant and LiBr-water as solution and the other is ammonia (NH 3 ) as refrigerant and water as solution. For air conditioning systems absorption refrigerating systems (AKA) with water/libr are used. The capacity range is between 15 KW and 10 MW. Absorption refrigerating systems (AKA) unit can be fired directly or indirectly. Directly fired systems work with natural gas, fuel oil, biogas or hot water. The worldwide most sold units of AKA type are directly fired. AKA units with a performance range between 15 kw and 300 kw are especially applicable for combined heat and power cycles (CHP). They are able to operate with lower temperatures (70 C 110 C). The economical importance consists especially in the ability to use waste heat with lower temperatures. Adsorption refrigerating systems (AdKA) work with two discontinuous cycles. In the first cycle, refrigerant vapour which is produced in the evaporator will be accumulating at the cooled sorption medium. In the second cycle, the sorption medium will be heated to drive out vapour. The emerging vapour will be conducted in the condenser to become liquid. The cycle is controlled by gate valves. Adsorption systems (AdKA) are able to work with very low heating temperatures on the one hand (55 C 95 C), achieve low coefficient of heating but are expensive on the other hand. Sorption medium is silica gel (silicon dioxide SiO2). As yet AdKA units installed in Germany are only offered by Japanese manufacturers. Less than a dozen adsorption systems (AdKA) are applied in Germany only. Open sorption methods, (DEC desiccant and evaporating cooling systems) Cooling by desiccation and evaporation. This means cooling of dried air by humidification with water. In a plant warm air will be sucked from outside and dehumidified. Afterwards the air will be re-cooled by heat exchanging with the exhaust air. The air is humidified before entering the room. A heater warms the exhaust air in the exhaust air flow, to regenerate the dehumidifier (dryer). Absorption chillers have the most important relevance referring heat driven refrigerating systems for air conditioning. Refrigerant is water; solution medium is LiBr-water-solution. This kind of systems is manufactured in large quantities and are offered world wide. Absorption Chillers are qualifying for the use of waste heat especially, but they can also be driven with vapour, natural gas, biogas, fermentation gas and liquid fuels. Table 3 compares different refrigeration methods. 16

17 Table 3: Methods of refigeration Methods of refrigeration for temperatures between 0 C and 15 C physical effect of refrigeration physical principe refrigerant evaporation evaporation evaporation in air to exhaust vapour by mechanical compressor to exhaust vapour by absorption in a (liquid solid) mechanical compression thermal compression thermal compression chemical or natural refrigerant sorbent - absorption adsorption H 2 O H 2 O H 2 O Li-Br H 2 O zeolith, silica gel. e. g. lithium chromat Table 4: refrigerating systems chiller with mechanical compressor absorption chiller adsorption chiller desiccant cooler KKA AKA AdKA DEC 1.Evaporation and Adsorption 2. Desorption and Condensation evaporator mech. compressor condenser expansion valve evaporator absorber generator condenser solution pump throttle valve expansion valve evaporator shut-off valve (closed) sorbent shut-off valve (opened) condenser vacuum pump enthalpy recovery wheel heat recovery Wheel humidifier heater 17

18 Table 5: parameters of refrigerating plants refrigerating plant compression absorption adsorption DEC operating power heating temperature electrical energy heat 70 C < t < 180 C heat 55 C < t < 95 C heat 40 C < t < 65 C refrigerating capacity/ drive capacity 4< COP K <6 0.65< ζ K < < ζ K < < ζ K <0.9 primary energy - efficiency 1.4< CO P K < < ζ K < < ζ K < < ζ K <0.81 ratio of cooling tower capacity and refrigerating capacity Q& 1.2< Q& K 0 < < Q& Q& K 0 Q& < < Q& K 0 < Trigeneration The trigeneratioin approach is quite new. The technology uses a combination of a cogeneration unit and absorption cooling unit maximize the utilization of cogeneration and using part of the heat to produce cooling. One of the main advantages of trigeneration is a prolonged period of effective yearly use. More effective cogeneration is based on using heat in summer, which is a main limiting element of classic cogeneration. Suitable summer use can be the absorption cooling, used for air-conditioning housing, administrative or technological objects. Main advantage of the absorption cooling unit is replacing the noble electrical energy input by less noble (and cheaper) heat energy. Another advantages (in comparison with compressor cooling units) are that it is quiet, simple, reliable and environment friendly. Technical conditions of trigeneration It is not easy to optimize the combination of cogeneration unit and absorption cooling because of the different parameters of heat circuits. The cogeneration units do best at 90/70 C and the absorption units have optimum high above 100 C. Increasing the parameters of the cogeneration units leads nearly always to decreasing the output and efficiency. The output of the absorption cooling is also decreased with decreasing temperature. So a compromise temperature has to be found in each particular implementation. It is usually between 100 and 110 C at the output of the cogeneration unit. Economical properties of trigeneration A way to increase economic efficiency is to split the output of the cooling units between absorption and compressor cooling. It is the same situation as with combination of cogeneration unit and peak-hours boilers it is good to combine capital-intensive absorption 18

19 and cheaper compressor cooling. The capital-intensive trigeneration is then optimized to cover the base consumption (electricity, heat and cooling) and the cheaper technologies cover the peak hours. 6. Technological solution Problems have to be solved when burning biogas off-site, in the place of consumption: Supplying the biogas plant with heat and electricity for self-consumption. Two solutions: 1. A small cogeneration unit optimized for the self-consumption of the plant (this is shown in the examples) 2. A gas boiler and electricity from distribution network Treatment and transport of gas Building the engine room for the cogeneration units off-site Securing consumption of electricity and heat during the whole year Energy utilization of biogas on-site and off-site In the text we will compare the advantages and disadvantages of on-site (in the place of production) and off-site (in the place of consumption) biogas utilization Economical efficiency By economical efficiency we mean investment return. On site: Lower investment Lower revenues (no revenues for heat) Simple accounting Lower operation costs Off-site: Higher investment Higher complexity of inner relations Gas treatment costs Costs of self-consumption heat and electricity source Costs of decreasing self-consumption of heat Economical efficiency off-site will be much higher, mainly due to greater revenues for selling heat and cooling. 19

20 Energy efficiency By energy efficiency we mean ratio of utilization of energy in fuel. Energy efficiency off-site will be more than twice higher. Amount of heat energy is in the case of cogeneration unit is higher, than the amount of electricity. Environmental efficiency It generally holds that production of higher form of energy (electricity) is accompanied by production of heat. By utilization of this heat can be achieved a better efficiency resulting in economical and environmental benefits. Environmental benefits Energy utilization of biogas on-site (biogas station) and off-site A. Comparison of centralized and decentralized electricity production B. Greenhouse gas and production efficiency problems Burning methane produces only half amount of CO 2 emissions compared to coal. Replacing the heat produced from brown coal with heat from gas engine results in saving of 1,3t of CO 2 in 1MWh of electricity. Replacing heat from natural gas with heat from gas engine results in saving of 1t of CO 2 in 1MWh of electricity. One permit for 1T of CO 2 costs ca. 20 EUR, that can help to objectively evaluate the benefits of lower emissions of cogeneration units. Higher utilization of energy in fuel results in fact in reduction of emissions otherwise produced in by sources. By environmental benefit we thus mean the ratio of emission reduction. 7. Comparison of economic parameters of heat and mechanical driven refrigerating processes The economic comparison of different refrigerating methods includes investment and operation costs (costs of energy and maintenance). Investment costs have to include refrigerating machine, cold and cool water cycle system, water conditioning, re-cool unit, electrical and controlling system and auxiliary equipment. The operation costs of refrigeration are determined by the local electricity costs ( /MWh) and the local water costs (fresh water and sewage). Heating costs are essentially for AKA units especially. Every cost calculation has to consider the specific local installation conditions. A special example will demonstrate the method of cost calculation including investment, operation and energy costs. A mechanical driven chillers and a single stage AKA unit are compared. The result of the cost calculation shows the energy costs for refrigeration [Euro / kwh]. The price of heat should not be more expensive than 1 Euro-Cent per kwh for same specific cost for refrigeration. The calculation of costs (Table 5) should help to find an orientation 20

21 only. However, heat driven refrigerating systems are more expensive than compression driven one. But it is possible to reach equal refrigerating costs, when the heat for driving an absorption system (AKA) can be provided to very low costs (e. g. waste heat from cogeneration unit). The economic benefit can be found often in better economy of a system of power, heat and cooling generation. Table 6: economic parameters of heat and mechanical driven refrigerating processes compression chiller absorption chiller consumption costs heating costs [ /kwh] 0.01 electrical power costs [ /kw/a] electrical energy costs [ /kwh] electrical total costs [ /kwh] sewage cost [ /m³] fresh water cost [ /m³] refrigerating capacity [kw] annual operation time [h/a] operation time [a] interest [%p.a.] COP [-] efficiency AKA Qo / Qh [-] annuity [%/a] 11% 11% investment specific investment for chiller [ /kw] specific investment for cooling tower, pumps, tubes and accessories *) [ /kw] specific investment [ /kw] investment costs [ ] 196, ,589 annual first costs [ /a] 22,189 38,314 operational costs maintenance [% of 1 st cost] 1.5% 1% maintenance costs [ /a] 2,950 3,396 electrical energy/heat costs [ /a] 72,917 41,438 fresh water costs [ /a] 11,745 23,035 sewage costs [ /a] 3,915 7,678 sum annual operating costs [ /a] 91,527 75,548 annual costs [ /a] 113, ,862 specifical annual costs of refrigeration [ /kwh] *) based on cooling tower capacity 21

22 8. Comparison of energetic parameters and CO 2 -emission of heat and mechanical driven refrigeration systems as well How much refrigerating energy can be got from 100 % primary energy? Table 6 answers this question by comparison of different methods of energy transformation. If the energy is transformed with a very good efficiency factor of 40 % in a power plant, then it is possible to obtain 160 % refrigeration energy from 100 % primary energy. The energy efficiency increases if a cogeneration process is used. It is possible to obtain up to 214 % energy efficiency from 100 % primary energy depending from the chosen process. In the case of transforming primary energy directly into heat for driving an absorption unit, only 108 % refrigeration energy can be obtained. The directly heated absorption unit uses primary energy worse as an absorption unit in cogeneration systems; and an electric driven refrigeration machines also. Table 7: energetic parameters of heat and mechanical driven refrigerating systems primary energy QBr energy transformation method efficiency of refrigeration Q o /Q Br Electricity Heat Waste Heat KKA AKA 100% condensation power station 40% 60% COP K =4 160% combined heat 100% and power plant 35% 55% 10% COPK = 4 ζ K = % CHP 100% co-generation unit 30% 60% 10% COPK = 4 ζ K = % 100% fuel cell 45% 45% 10% COP K = 4 ζ K = % 100% heat Plant oil/ natural gas 90% 10% ζ K = % 22

23 9. Examples and calculations Other properties of cogeneration units A great benefit of cogeneration units with gas engines is their high electrical efficiency and simple utilization of heat. The heat from engine and oil cooling is lead by the primary circuit by a simple exchanger (water water). The cooling of burnt gas is also much more simple than in turbines (which are sensitive to counter pressure the exchanger has to be quite large and expensive). The amount of electricity and usable heat produced in a unit of time divided by the amount of consumed fuel gives the total efficiency of the cogeneration unit. The assumptions will be further proved in two examples. Both are biogas plants. Basic assumptions: BGP with local utilization of biogas by burning in a cogeneration unit Biogas used in cogeneration sets with piston engines All the energy produced is supplied to network (sold) The heat for self-consumption is taken from cogeneration Emission factors for heat are meant as a mix (1/1) of coal and gas source Technology problems are not a subject of this study The unconsumed heat is marred in coolers. Example 1 Option 1a - on-site Installed capacity: 555kW one cogeneration unit 23

24 Table 8: Option 1a Biogas production [Nm 3 ] Yearly production of methane [Nm 3 ] Heating power [kwh/m 3 ] 10 Gross energy [MWh/year] Option Cogeneration Parameters 1a on-site DEUTZ TCG 2016 B V12 Engine power [kw] 555 Installed generator capacity [kw] 537 Efficiency Total 90,5% Heat 55,3% Electrical 35,2% Output balance Total theoretical output [kw] 1297 Total output [kw] of that electrical output [kw] 457 heat output [kw] 717 Energy balance Energy input in fuel [MWh/year] Self-consumption Electricity (4%) [MWh/year] 146 Heat (20%) [MWh/year] 764 Energy output from CU [MWh/year] of that Electrical energy [MWh/year] of that Heat - cooling water [MWh/year] Usable energy Heat [MWh/year] Electricity [MWh/year] Utilized energy Heat [MWh/year] 0 Electricity [MWh/year] Total efficiency 34% 24

25 Option 1b off-site: Installed capacity: 640kW two cogeneration units, 85kW self-consumption, 555kW off-eide Table 9: Option 1b Biogas production [Nm 3 ] Yearly production of methane [Nm 3 ] heating power [kwh/m 3 ] 10 gross energy [MWh/year] Option 1b Cogeneration on-site off-site Parameters TEDOM CENTO 180 DEUTZ TCG 2016 B V12 Engine power [kw] Installed generator capacity [kw] Efficiency Total 89,3% 90,5% Heat 56,1% 55,3% Electrical 33,2% 35,2% Output balance Total theoretical output [kw] Total output [kw] of that electrical output [kw] heat output [kw] Energy balance Energy input in fuel [MWh/year] Self-consumption Electricity (4%) [MWh/year] Heat (20%) [MWh/year] Energy output from CU [MWh/year] of that Electrical energy [MWh/year] of that Heat - cooling water [MWh/year] Usable energy Heat [MWh/year] Electricity [MWh/year] Utilized energy Heat [MWh/year] Electricity [MWh/year] Total efficiency 82% 25

26 Example 2 Option 2a - on-site Installed capacity: 2220kW three cogeneration units Table 10: Option 2a Option Cogeneration Parameters Biogas production [Nm 3 ] Yearly production of methane [Nm 3 ] heating power [kwh/m 3 ] 10 gross energy [MWh/year] on-site DEUTZ TCG 2016 B V16 2a DEUTZ TCG 2016 B V16 DEUTZ TCG 2016 B V16 Engine power [kw] Installed generator capacity [kw] Efficiency Output balance Total 91,1% 91,1% 91,1% Heat 54,8% 54,8% 54,8% Electrical 36,3% 36,3% 36,3% Total theoretical output [kw] Total output [kw] of that electrical output [kw] Energy balance Total heat output [kw] Energy input in fuel [MWh/year] Self-consumption Electricity (4%) [MWh/year] Heat (20%) [MWh/year] Energy output from CU [MWh/year] of that Electrical energy [MWh/year] Heat - cooling of that water [MWh/year] Usable energy Heat [MWh/year] Electricity [MWh/year] Utilized energy Heat [MWh/year] Electricity [MWh/year] Total efficiency 35% 26

27 Option 2b - off-site Installed capacity: 2400kW four cogeneration units, 180kW self-consumption, 3 x 740kW off-site Table 11: Option 2b Biogas [Nm 3 ] production Yearly production of [Nm 3 ] methane heating power [kwh/m 3 ] 10 gross energy [MWh/year] Option Cogeneration on-site off-site DEUTZ DEUTZ TCG 2016 TCG 2016 Parameters B V12 B V16 2b DEUTZ TCG 2016 B V16 DEUTZ TCG 2016 B V16 Engine power [kw] Installed generator capacity [kw] Efficiency Total 90,1% 91,1% 91,1% 91,1% Heat 55,3% 54,8% 54,8% 54,8% Electrical 34,8% 36,3% 36,3% 36,3% Output balance Total theoretical output [kw] Total output [kw] of that electrical output [kw] heat output [kw] Energy balance Energy input in fuel [MWh/year] Total Self-consumption Electricity (4%) [MWh/year] Heat (20%) [MWh/year] Energy output from CU [MWh/year] of that Electrical energy [MWh/year] of that Heat - cooling water [MWh/year] Usable energy Heat [MWh/year] Electricity [MWh/year] Utilized energy Heat [MWh/year] Electricity [MWh/year] Total efficiency 85% 27

28 Results of calculation Energy comparison The biogas utilization efficiency is more than twice as higher off-site, the results can be seen in following tables and graphs. Example 1 Table 12: Example 1 Option 1 on-site off-site Energy input in fuel [MWh/year] Self-consumption - heat [MWh/year] Self-consumption - electricity [MWh/year] Total self-consumption [MWh/year] Heat distribution [MWh/year] Electricity distribution [MWh/year] Unused energy [MWh/year] Total energy supply [MWh/year] Utilization of the energy in fuel 34% 82% 28

29 Image 6: Energy Efficiency Energy efficiency Unused energy Electicity distribution Heat distribution Self-consuption - electricity Self-consumtion - heat

30 Example 2 Table 13: Example 2 Option 1 on-site off-site Energy input in fuel [MWh/year] Self-consumption - heat [MWh/year] Self-consumption - electricity [MWh/year] Total self-consumption [MWh/year] Heat distribution [MWh/year] Electricity distribution [MWh/year] Unused energy [MWh/year] Total energy supply [MWh/year] Utilization of the energy in fuel 35% 85% Image 7: Energy Efficiency Energy efficiency Unused energy Electicity distribution Heat distribution Self-consuption - electricity Self-consumtion - heat