Potential for Absorption Cooling
Generated from Municipal Solid Waste in Bangkok
A Comparison between Waste Incineration &
Biogas Production with Combustion
Erika Hedberg
Helén Danielsson
Environmental Technology and Management
Degree Project
Department of Management and Engineering
LIU‐IEI‐TEK‐A‐‐10/00807‐‐SE
Abstract
This master’s thesis has been performed in Bangkok, Thailand at the company Eco Design Consultant Co., Ltd. The aim is to investigate the possibilities to generate absorption cooling from municipal solid waste in the Bangkok area. The investigation includes a comparison between waste incineration and biogas production with combustion to see which alternative is preferable. During the investigation, a Swedish perspective has been used.The research for the report mainly consisted of published scientific articles from acknowledged sources as well as information from different Thai authorities. Also, experts within different areas were contacted and interviewed. In order to determine which of the two techniques (waste incineration or biogas production with combustion) that is best suited to generate absorption cooling, a model was designed. This model involved several parameters regarding e.g. plant efficiency, amount of treated waste and internal heat usage. As for the results of the model, three parameters were calculated: the generated cooling, the net electricity generation and the reduced greenhouse emissions.
The overall Thai municipal solid waste generation in Thailand is estimated to approximately 15 million tons per year and the majority of the waste ends up at open dumps or landfills. There are only two to three waste incinerators in the country and a few projects with biogas generation from municipal solid waste. The main electricity is today generated from natural gas which makes the majority of the Thai electricity production fossil fuel based. As for absorption cooling, two applications of this technique has been found in Thailand during the research; one at the Naresuan University and one at the Suvarnabhumi airport in Bangkok.
The model resulted in that the best alternative to power absorption cooling technique is waste incineration. This alternative has potential to generate 3200 GWh cooling per year and 1100 GWh electricity per year. Also, this alternative resulted in the largest decrease of greenhouse gas emissions, ‐500 000 tons per year. The model also showed that the same amounts of generated cooling and electricity can never be achieved from biogas production with combustion compared to waste incineration. Regardless, waste incineration has an important drawback: the citizens of Thailand seem to oppose further development of waste incineration in the country. The biogas technique seems more approved in Thailand, which benefits this alternative. Due to the high moisture and organic content in the municipal solid waste, a combination between the two waste handling alternatives is suggested. This way, the most energy can be withdrawn from the waste and the volume of disposed waste is minimized.
Our overall conclusion is that the absorption cooling technique has great potential in Thailand. There is an increasing power‐ and cooling demand, absorption cooling generated from either or both of the alternatives can satisfy these demands while reducing greenhouse gas emissions. We also believes that the cost for using absorption cooling has to be lower than for the current compression cooling if the new technique is to be implemented further.
Acknowledgements
We would like to express our gratitude to the persons that have assisted and helped us in different ways during the process of writing this thesis. In no particular order, the persons we want thank are: Mattias Lindahl, our supervisor who has guided us during this entire process and has offered his knowledge and support. Dr Akajate Apikajornsin and Dr. Prin Boonkanit who welcomed us to Thailand and to Eco Group Co. Ltd., and have assisted us during our research in Bangkok. The respondents of our interviews, for taking their time to answer our questions and presenting the practical perspectives of the researched areas. We have found all of the interviews very interesting. Our opponents Andres Adelmann and Sissela Lidebjer for useful feedback and comments.
Louise Trygg, who has offered interesting input and guided us when there has been confusing moments. Our colleagues at Eco Group Co. Ltd. who all have assisted in welcoming us and assisting in different ways during our research, but also for making our time in Bangkok interesting and entertaining. Thank you! Erika Hedberg & Helén Danielsson Linköping 26th May 2010
Table of Contents
1 Introduction ... 1 1.1 Background ... 1 1.2 Purpose ... 1 1.3 Limitations ... 2 2 Method ... 3 2.1 Model ... 3 2.2 Interviews ... 3 3 Theoretical Frame of Reference ... 5 3.1 Thailand ... 5 3.2 The Global Warming and the Greenhouse Effect ... 5 3.3 Combined Heat and Power ... 5 3.3.1 CHP in Sweden ... 6 3.4 Waste Management ... 7 3.4.1 Waste Handling in Sweden ... 7 3.5 Landfills and Open Dumps ... 8 3.6 Waste Incineration ... 8 3.6.1 Flue Gas Purification and Residuals ... 9 3.6.2 Waste Incineration in Sweden ... 9 3.7 Biogas ... 10 3.7.1 Production ... 10 3.7.2 Combustion of Biogas ... 11 3.7.3 Biogas in Sweden ... 11 3.8 Environmental Aspects of Waste Management Techniques ... 11 3.8.1 Landfilling and Open Dumping ... 11 3.8.2 Waste Incineration ... 12 3.8.3 Biogas ... 12 3.9 District Heating and Cooling ... 13 3.10 Compression Cooling ... 14 3.11 Absorption Cooling ... 15 3.11.1 Distribution ... 16 3.11.2 The Absorption Cooling Machine ... 16 3.12 Efficiency of ACM Compared to CCM ... 183.13.1 Price Development ... 20 3.13.2 CHP and Absorption Cooling in the Swedish Energy System ... 21 4 Results ... 23 4.1 Interviews ... 23 4.1.1 Situation in Bangkok ... 23 4.2 Waste Management in Thailand ... 24 4.2.1 Waste Situation ... 24 4.2.2 Waste Development ... 24 4.2.3 The Waste Composition ... 26 4.2.4 Waste Incineration in Thailand ... 26 4.2.5 Biogas in Thailand ... 27 4.3 The Thai Power Generation and Electricity Market ... 28 4.3.1 The Authorities ... 29 4.3.2 Private Participation ... 29 4.3.3 Independent, Small and Very Small Power Producers ... 30 4.3.4 Electricity Prices and Price Development ... 31 4.3.5 Renewable Energy in Thailand ... 32 4.3.6 Thailand Power Development Plan ... 33 4.4 Absorption Cooling in Thailand ... 34 5 Model ... 37 5.1 In‐Parameters ... 38 5.2 Waste Incineration ... 39 5.2.1 Energy Content and Torch Fuel Usage ... 39 5.2.2 Electricity and Heat Generation ... 40 5.2.3 Internal Energy Usage and Net Energy Output ... 41 5.3 Biogas Production and Combustion ... 41 5.3.1 Organic Fraction of MSW and Sorting Percentage ... 42 5.3.2 Electricity and Heat Generation ... 42 5.3.3 Internal Energy Usage and Net Energy Output ... 43 5.4 Absorption Cooling ... 44 5.4.1 Generated from Waste Incineration ... 44 5.4.2 Generated from Biogas Combustion ... 44 5.5 Greenhouse Gas Emissions ... 44 5.5.1 Waste Incineration ... 45
5.5.2 Biogas Production and Combustion ... 48 5.6 Results from the Model ... 50 5.7 Sensitivity Analysis ... 50 5.7.1 Percentage of Collected Waste ... 50 5.7.2 Efficiencies Waste Incineration ... 51 5.7.3 Energy Input Waste Incineration ... 51 5.7.4 Sorting Percentage Biogas Process & Biogas Yield ... 51 5.7.5 Efficiencies Biogas Production and Combustion ... 51 5.7.6 Energy Input Biogas Production and Combustion ... 52 5.7.7 Chiller Parameters ... 52 5.7.8 Organic Fraction and Calorific Value of MSW ... 52 6 Analysis ... 55 6.1 Data Collection ... 55 6.2 Energy Situation and Energy Development in Thailand ... 56 6.3 The Thai Waste Situation ... 56 6.3.1 Waste Development ... 57 6.4 Waste Incineration ... 57 6.5 Biogas Production and Combustion ... 58 6.6 Absorption Cooling and Distribution ... 58 6.6.1 Cooling Recipients ... 59 6.7 The Thai Electricity Market, Prices and Costs ... 60 6.7.1 Investors ... 61 6.8 Model ... 62 6.8.1 Results from the Model ... 63 6.8.2 Sensitity Analysis ... 64 6.9 Feasibility in Bangkok ... 67 7 Conclusions ... 69 8 Further Research ... 71 9 List of References ... 73 9.1 Printed sources ... 73 9.2 Web Based Sources ... 75 9.3 Personal Sources ... 81 10 Appendix ... 83
List of Figures
Figure 3‐1 ‐ Schematic picture displaying difference between Combined Heat and Power Production and Power Production ... 6 Figure 3‐2‐ The EU Waste Hierarchy ... 7 Figure 3‐3 – Waste treatment in Sweden distributed on different treatment methods ... 8 Figure 3‐4 – Waste incineration process ... 9 Figure 3‐5 – The biogas production steps ... 10 Figure 3‐6 ‐ Schedule displaying compression cooling and absorption cooling ... 16 Figure 3‐7 – Comparison of Carnot‐factor for compressor cooling and absorption cooling ... 19 Figure 3‐8 – Price development of the Swedish electricity price, no taxes included. ... 21 Figure 4‐1 – Tones of waste generated in Thailand 1998‐2006 ... 25 Figure 4‐2 – The amount of generated waste in Bangkok 1998‐2006 ... 25 Figure 4‐3 ‐ Thailand’s Fuel Mix for Power Generation (Jan 2010). ... 28 Figure 4‐4 ‐ Thailand’s Electricity Industry Structure ... 31 Figure 4‐5 ‐ New power project investments for 2008‐2021 presented in MW ... 34 Figure 5‐1 – A schematic figure of the different flows in the model ... 37 Figure 10‐1 – Treatment of waste generated from manufacturing production in Sweden ... 83 Figure 10‐2 – Waste composition of MSW in weight percent for Sweden ... 83 Figure 10‐3 – Waste composition of MSW in percent of total for Thailand ... 84 Figure 10‐4 – Percent of used energy in Thailand 1986‐2009 ... 84 Figure 10‐5 – Electricity bill for a one room apartment in Bangkok ... 85List of Tables
Table 3‐1 – Estimated characteristics for different ACMs ... 17 Table 4‐1 “Adder” to the Normal Tariff for SPPs and VSPPs ... 30 Table 5‐1 –Results from Model ... 50 Table 10‐1 – Alteration of Percentage Organic Fraction ... 86 Table 10‐2 – Alteration of Calorific Value MSW ... 87 Table 10‐3 – Alteration of Electric Efficiency Waste Incineration ... 88 Table 10‐4 – Alteration of Heat Efficiency Waste Incineration ... 89 Table 10‐5 – Alteration of Internal Electricity Usage Waste Incineration ... 90 Table 10‐6 – Alteration of Sorting Percentage Biogas Production ... 91 Table 10‐7 – Alteration of Biogas Yield ... 92 Table 10‐8 – Alteration of Electric Efficiency Biogas Combustion ... 93 Table 10‐9 – Alteration of Thermal Efficiency Biogas Combustion ... 94 Table 10‐10 – Alteration of Internal Electricity Usage Biogas Production & Combustion ... 95 Table 10‐11 – Alteration of Internal Heat Usage Biogas Production & Combustion ... 96 Table 10‐12 – Alteration of Percentage of Collected Waste ... 97 Table 10‐13 – Alteration of COP Absorption Chiller ... 98 Table 10‐14 – Alteration of COP Compression Chiller ... 99 Table 10‐15 – Alteration of Torch Fuel Waste Incineration ... 100Abbreviations
ACM Absorption Cooling Machine AOB Airport Operation Building BAT Best Available Technology BMA Bangkok Metropolitan Administration CCM Compressor Cooling Machine CFC Chlorofluorocarbon CHP Combined Heat and Power CO₂ Carbon Dioxide CO2 eq. Carbon Dioxide Equivalents COP Coefficient of Performance CTF Clean Technology Fund DCAP District Cooling System and Power Plant Co., Ltd. EGAT Electricity Generating Authority of Thailand EPPO Energy Policy and Planning Office (Thailand) ERC Energy Regulatory Commission (Thailand) EU European Union GHG Greenhouse Gas GWP Global Warming Potential HCFC Hydrochlorofluorocarbon IPP Independent Power Producers (Thailand) MEA Metropolitan Electricity Authority (Thailand) MSW Municipal Solid Waste NEPC National Energy Policy Council (Thailand) NG Natural Gas OFMSW Organic Fraction of Municipal Solid Waste PCD Pollution Control Department (Thailand) PDP Power Development Plan (Thailand) PEA Provincial Electricity Authority (Thailand) PTT Petroleum Authority of Thailand RQ Research Question SEK Swedish krona (currency of Sweden) SO₂ Sulfur Dioxide THB Thai bath (currency of Thailand) TNSO/NSO The National Statistic Office (Thailand) TOU Time of Use VAT Value Added Tax VSPP Very Small Power Producers (Thailand) WTE Waste to Energy1
Introduction
The introduction part will give a short background as to why the subject of this thesis is interesting, as well as the purpose of the thesis and an explanation of the limitations that has been made.
1.1 Background
It is getting more and more important to save energy and to use a wiser energy approach due to the current environmental situation. It is important to use energy, materials and fuels in a sustainable way; generating energy from waste is one way to recover the energy in the waste. Today, large volumes of waste are however put on landfills and open dumps. This way the potential of using the energy is lost and huge areas are occupied by waste.
Since 2002 it is forbidden to landfill combustible materials in Sweden. Instead, the majority of the waste is incinerated and at some incineration plants the energy is recovered through electricity and/or heat generation. The heat is mostly used as district heating, and sometimes cooling.
The organic fraction of the waste can be transformed into energy in the form of biogas as well. When organic materials are digested without oxygen, biogas is produced.
In Thailand, the waste management is rather different than in Sweden. The majority of the waste is put on open dumps and only a fraction is incinerated. This generates large volumes of waste and unused resources. Thailand is also, unlike Sweden, a tropical country with warm temperature. The capital city, Bangkok, has an average temperature over 25 °C during the entire year. Due to the high temperature, the Thai people have a large cooling demand. This demand is today mostly generated by electricity‐driven cooling machines.
Absorption cooling machines are in contrast to compression cooling machines, driven by heat instead of electricity. Combined heat and power generation, together with absorption cooling machines, therefore offers an interesting alternative to produce cooling when it comes to achieving a decrease of carbon dioxide emissions.
1.2 Purpose
The purpose of this master’s thesis is to investigate the possibilities for absorption cooling generated from municipal solid waste in Bangkok. Waste incineration will be compared with biogas production and combustion as driving force for the absorption cooling. The questions at aim together with short explanations of their relevance are presented below: RQ1. Is absorption cooling generated from MSW an alternative to replace a part of the compression cooling in Bangkok? Would this achieve a decrease in GHG emissions?Absorption cooling is a technique that under certain circumstances offers cooling with less GHG emission than compression cooling. This fact combined with the large amount of generated waste in the region and the big use of compression cooling makes this question relevant. RQ2. Which alternative would generate the largest GHG emission reduction if used to drive the absorption cooling; waste incineration or biogas production with combustion? What other factors affect the comparison of the alternatives, and how?
Both these alternatives offer ways of driving the absorption cooling with waste as input. Since the processes are so different they need to be evaluated toughly to know which would decrease the GHG emissions more than the other, compared using compression cooling. RQ3. What other factors, environmental, technical as well as societal, needs to be taken into consideration if absorption cooling generated from MSW would constitute a relevant option? The answers to question number one as well as question number two might only be true under certain circumstances. These circumstances need to be identified.
1.3 Limitations
To perform this investigation a number of limitations need to be made so that the analyzed system does not become too large. Since the analysis includes many different systems the approach will first and foremost be a system view. Due to this system view the investigation of technical details will not be very specific.A model will be used to perform a comparison between waste incineration and biogas production
with combustion. This model is a simple model used to compare the two alternatives from a system
view. Specific limitations made in the model are explained further in Chapter 5. To compensate for some of these limitations, a sensitivity analysis will be performed. The sensitivity analysis will show what impact some of the simplifications and assumptions have had on the results.
Regarding the generated waste in Bangkok, this will only be considered as potential energy, the possibilities regarding recycling will not be evaluated. This could affect both the answers to RQ1 and RQ2. If recycling was an alternative, this might be more desirable than to use the waste for producing cooling. If recycling was performed, the amount of waste available after recycling could decrease significantly and the content of the waste available after recycling could also change considerably. These changes would alter the conditions for both biogas production and waste incineration, which in turn would affect the conditions for the absorption cooling in RQ1. The comparison in RQ2 will probably not be affected to the same extent, since RQ2 is a comparison between processes based on the same input. Although a change in waste content would change the conditions for the processes in different ways.
The reasonability and details of distributing absorption cooling in Bangkok will be limited. Bangkok is a big area and an analysis of the distribution possibilities and details is too large to all be included since Bangkok does not have any district heating or cooling networks at the moment. Since the distribution needs to be managed in one way or another, this could affect the answer to RQ1. It is however assumed that the distribution can be handled somehow, there are many examples of densely populated cities that have district heating or cooling and Bangkok is not considered to be different from these. It is rather a question of how much this would cost, and how complicated the process would be. If using CHP production from either waste incineration or biogas combustion, the generated heat will only be considered as a potential heat source for absorption cooling.
2
Method
To answer the questions at issue and to reach the purpose of this master’s thesis, a series of steps will be taken. The first step will be to perform a literature study where relevant literature, articles and reports on the subject are read and summarized in a theoretical frame of reference. This step will be preformed to achieve a greater knowledge in the different energy and environmental areas. The next step will be to research the relevant systems in Bangkok and Thailand, including literature studies, observations and interviews. This work will be performed at the consulting‐firm Thai company called Eco Group Co. Ltd. in Bangkok. The results from the research regarding the systems in Bangkok will be presented as results. The interview methods are further explained in chapter 2.2. Another step of the process will be to make a model of a system in Bangkok. Based on this model calculations and/or simulations will be made, in order to determine the effects of using absorption cooling, and to decide whether waste incineration or biogas production and combustion is the best option. The method for the model is explained further in chapter 2.1. When sufficient amounts of material, as well as results from the model, are gathered, this will lead to results. The results will be analyzed and discussed, and will finally result in conclusions and give answers to the questions at issue.
The project will have a Swedish perspective and in the analysis part comparisons will be made between the Swedish and Thai waste and energy systems. This is because the idea for this thesis originates from a Swedish perspective and it is important to identify the differences between the energy systems in the countries. Therefore this perspective will be maintained throughout the work, especially when investigating the plausibility for the techniques in Thailand. The Swedish perspective will not be as present in the comparison in the model. The target audience for this report is mainly Thai citizens. Therefore the Swedish energy systems and waste management will be presented rather thoroughly, in order to give the reader an understanding for the Swedish perspective.
2.1 Model
A model will be constructed in order to compare the GHG emissions and the generated energy from the two different waste management alternatives suggested. The model will be performed in MS Excel and the calculations, as well as results, will be presented in the thesis. The different waste management alternatives will share the same in‐parameters and a sensitivity analysis will be made in order to investigate the parameters dependence.2.2 Interviews
A part of the investigation will involve personal interviews. The interviews will be considered as a more precise source of information regarding the areas where information has been lacking. Since the report investigates different energy and environmental areas, the interviewed persons will be local experts in these different areas. Therefore, the questions will be different for each interview and designed to achieve as precise information as possible. Before the interview, the investigated area will be studied and evaluated.
During the interviews, one person will be asking the questions and another person will be taking notes. After the interview the obtained answers will be discussed and evaluated as soon as possible
considered as open and there will be no restrictions against attendant questions. Instead, discussions will be welcomed to evolve new and interesting questions on the current subject. There are no restrictions for the length of the interviews; the main intention is to achieve answers as extensive as possible.
3
Theoretical Frame of Reference
To be able to present the results of the thesis in a comprehensive way, some background information is necessary. Different technical solutions such as combined heat and power, biogas production, waste incineration, district cooling and different cooling techniques are addressed. Information regarding different energy systems that are relevant are also included, as well as facts about waste management systems and the environmental aspects of these different waste management systems. Regarding the different cooling techniques the absorption cooling is the most extensive. The theoretical frame of reference contains mostly information about the Swedish energy systems, techniques and waste management, while facts about the systems in Thailand are presented in Chapter 4, except for a short introduction of Thailand.
3.1 Thailand
Thailand, previously Siam, is a country in the southeast of Asia. The country is 513 115 km² and is separated into 76 provinces. The nation has 66.1 million inhabitants and the population is expected to be close to 70 million in 2050. The main capital, Bangkok, has 5.7 million inhabitants. (Nationalencyklopedin 2010a)
Thailand mainly has a tropical monsoonal climate although in the south part, the climate consists of tropic rainforest with two rain seasons. The warmest period is between March and April and the yearly average temperature is 24‐30 °C for the entire country. (Nationalencyklopedin 2010a)
The currency in Thailand is Thai baht (THB). The value of the baht is 0.223 Swedish kronor (SEK). (Riksbanken 2010) One baht equals 100 satang. The value of the baht in relation to the US dollar is one dollar equals 31.36 THB. (Thaivisa 2010) These values are valid for 22nd of April 2010 and will be used throughout the thesis.
3.2 The Global Warming and the Greenhouse Effect
The global warming refers to the increased average temperature on Earth during the last hundred years. One of the most accepted explanations to this phenomenon is the emissions of greenhouse gases made by the humans. The greenhouse effect is when greenhouse gases, such as carbon dioxide, methane, dinitrogen oxide and fluorine compounds lay around the Earth and effect the out flowing heat balance. This effect exists naturally and without it the Earth would be about 35 °C colder. However, the effect has been amplified by the greenhouse gas emissions from the humans, mainly originating from combustion of fossil fuels. This has led to an increased average temperature on the Earth. (Miljöportalen 2010)
3.3 Combined Heat and Power
Combined heat and power (CHP), also known as co‐generation, refers to the process of simultaneous production of heat and power. A CHP plant uses the heat that goes to waste when only producing electricity. The heat produced is used for district heating, industry application or in other ways. When using CHP production, 80‐90% of the energy content in the fuel can be used instead of only approximately 50% which is the maximum when only producing electricity in thermal power plants. (Nationalencyklopedin 2010b)Figure 3‐1 shows a schematic picture of a comparison between a CHP plant and a power plant. It displays the possibilities to use the heat from a CHP plant for district heating and/or absorption cooling through district heating or other applications instead of simply using a cooling tower to remove the heat.
Figure 3‐1 ‐ Schematic picture displaying difference between Combined Heat and Power Production and Power
Production (adapted from Karlsson 2008)
The traditional type of CHP plant is a steam power station. Gas turbines and a combination of a gas turbine and a steam power station, a combination cycle, are also common. A common way of producing only power, i.e. when the heat is not used, is through condensing power plants. (Nationalencyklopedin 2010b)
The fuel type used in CHP plants differs according to fuel access, boiler type, etcetera. Commonly used fuels are natural gas, oil, coal, biofuel and municipal solid waste. (Svensk Fjärrvärme 2010a) In Sweden, the municipalities are responsible for collecting, transporting and treating the MSW generated in their region. The municipalities do however charge for this service. (Nationalencyklopedin 2010c)
3.3.1 CHP in Sweden
Since Sweden has a varying climate, the heat demand varies a lot over the year. About 95% of the heat produced in CHP plants is used in district heating grids. (Avfall Sverige 2009a) Many Swedish CHP plants are run by natural gas or biofuels. (Svensk Fjärrvärme 2009)
The energy generation in a CHP plant involves energy losses like all energy transformations, although they are not as great as when only producing electricity. For every two TWh of fuel, a standard
Swedish CHP plant generates approximately 1.1 TWh of heat and 0.6 TWh of electricity. That means that the total energy losses are approximately 15%. (ÅF Energi och Miljöfakta 2010a)
3.4 Waste Management
All countries in the world generate waste. Waste is classified as material that the owner wants to, or is responsible to, disposes of. The previous definition is from the Environmental Code in Sweden and it is the same all over the European Union. (Nationalencyklopedin 2010c)There are a several ways of handling waste. Elements such as economy, environmental awareness and political management control measures determine the country’s waste management. (Sundberg 2008) Sweden, for example, follows the EU’s framework directive for waste handling, the waste
hierarchy. According to this, the waste should be taken care of in the following order; reduce, reuse, recycle, recover and dispose, as displayed in Figure 3‐2.
One way of treating waste is to reuse the energy in the refuse material. This is called waste‐to‐energy (WTE) and waste incineration plant with heat‐ or/and electricity generation is one example of this approach as well as biogas production with combustion. (Sundberg 2008)
3.4.1 Waste Handling in Sweden
Since 2002, there is a ban against landfilling combustible materials in Sweden. The ban was expanded in 2005 to also include landfilling of organic waste, with some exceptions. (Naturvårdsverket 2009a)
Between the years of 1994‐2006 the number of landfills in Sweden decreased from 300 to 160. This number will continue to decrease in the future due to stricter laws. (Avfall Sverige 2009b) Today there are about 260 larger waste treatment plants in Sweden where about one hundred of them are landfills, thirty uses waste combustion with energy and heat recovery and about forty are biological treatment plants. Figure 10‐1 in Appendix shows the current situation regarding the waste treatment methods for the Swedish manufacturing production. Figure 3‐3 shows the history for the different treatment methods for the years 2000‐2008. (ÅF Energi och Miljöfakta 2010b) During 2006, the amount of generated non‐hazardous waste in Sweden was about 121 million tones. (Naturvårdsverket 2009b)
The ban against landfilling combustible and organic waste has led to an increased amount of incinerated waste and an increased amount of energy generated from the combustion process. In
2007, about 4% of the waste in Sweden was landfilled. (ÅF Energi och Miljöfakta 2010d) Since the ban of landfilling organic waste, the biological treatment has increased over the past years. The year of 2007, approximately 561 000 tons of MSW was treated biologically. This number represented 11.9% of the total amount of treated MSW. (Avfall Sverige 2009c) Figure 3‐3 – Waste treatment in Sweden distributed on different treatment methods (adapted from ÅF Energi och Miljöfakta 2010b)
3.5 Landfills and Open Dumps
One of the most common ways of handling disposed material is to put it on landfills or open dumps. There is a difference between sanitary landfilling and open dumping; on an open dump, the waste is disposed without further treatment. (Encyclopædia Britannica 2010b) Open dumping and landfilling cause methane leakage into the atmosphere and can also cause leakage to ground water, human diseases, odor and large dioxin emissions due to landfill fires. On sanitary landfills the waste is put in several thin layers with soil covering the waste layers. All the layers are packed with heavy machinery to prevent settling, odor and leakage. The possibilities for landfill fires are also minimized when using sanitary landfilling. (Avfall Sverige 2009d)3.6 Waste Incineration
There are mainly two different ways of incinerating waste material, grate firing and fluidized bed combustion. (ÅF Energi och Miljöfakta 2010c) When using grate firing, the waste is loaded into the fire and the material is sparked. (Tekniska Verken 2009a) When using fluidized‐bed combustion, the bed contains reactive or inert particles (a sand bed) which, together with strong up flowing air, makes the bed behave like a turbulent fluid. The material is said to be floating. (ÅF Energi och Miljöfakta 2010e) This type of combustion is commonly used when having a fuel that is of low quality, i.e. fuel that is difficult to burn. It is also well adapted for combustion with different waste materials and it is sometimes used for combustion of coal and peat. (Access Science 2010a) Regarding the electric efficiency of waste incineration plants, larger plants are more effective than smaller. (Grosso, Motta & Rigamonti 2010)
Figure 3‐4 shows a simplified example of a waste incineration plant with energy recovery in form of electricity generation. At (1) the waste is tipped into a bunker where a crane picks it up and transports the waste into a hopper (2). The waste is then continuously loaded into the incinerator (3). Inside the incinerator, the heat is used for the boiler where the steamed water later in the
bottom ash is collected (5) and an electromagnet is used to separate the metal from the ash. To clean the flue gases from fine ash, SO₂ and dioxins, the smoke has to pass to a cleaning system with a scrubber reactor (6). In (7), the gas has to pass through a fine particulate removal system. The gas is then released through the chimney (8). (BBC NEWS 2010) Figure 3‐4 – Waste incineration process (BBC NEWS 2006) 3.6.1 Flue Gas Purification and Residuals When incinerating the waste, there are several toxic pollutions that have to be taken care of before releasing the gas out in the air. There is a condensation process, in which both gaseous (e.g. sulfur dioxide, phenol) and stable forms (e.g.. metal dust) of pollutions are separated from the gas. There are normally two purification processes; one dry and one wet step. (Naturvårdsverket 1993) In the first step, dry flue gas purification, the process is to separate the dust from the gases. This is done by letting the gas pass a textile filter. Before the gas enters the filters, active coal and calk are added so that heavy metals, dioxins etcetera are captured. The dust is then collected in a special silo. For the wet flue gas purification process, the chimney gases are washed with water. This is made in two cleaning steps and one heat recycling step. In these steps sulfur, ammonia, heavy metals and chlorides are removed and in the last step the heat from the chimney gases is taken care of. After the cleaning processes, the chimney gas is sent out to the air. (Tekniska Verken 2009b) When waste is incinerated, there are some residuals left. The slag products, mainly fly ash, soil ash and non‐burnt material, are transported from the boiler for further recycling or reusing. Metals such as iron are separated with magnets and are recycled. In Sweden, the slag gravel is used for replacing natural material in the building sector. There are also toxic residuals that have to be safely landfilled in special cells. (Naturvårdsverket 1993) 3.6.2 Waste Incineration in Sweden
The incineration plants in Sweden normally use different waste materials according to supply, combustion capacity, etcetera. Since Sweden has cold temperatures and a large heat demand during the winter, incineration plants with co‐generation sometimes use different fuels during peak seasons. The most common fuel at Swedish waste incineration plants is household waste, approximately 60%. (Avfall Sverige 2009e) Other rather common materials used for combustion are industrial waste, construction material, demolished tires and wood residuals. The amount of energy in one ton of Swedish household waste is about three MWh. (Naturvårdsverket 2010a) For further information regarding the Swedish composition of MSW, see Figure 10‐2 in Appendix.
The waste incineration in Sweden contributes with 20% of the energy to the district heating grid. (Avfall Sverige 2009f) 6% of the electricity consumed in Sweden originates from CHP plants (Svensk Fjärrvärme 2010b) and 0.3% of the total electrical energy produced in Sweden originates from waste incineration (Avfall Sverige 2009f). During 2007 13.6 TWh of district heating and electricity were produced from waste incineration in Sweden. (ÅF Energi och Miljöfakta 2010b)
3.7 Biogas
Another way of waste management is biogas production. Biogas consists, like natural gas, mainly of methane gas but there is a difference in the weight and in the production. Biogas is generated from organic materials while natural gas is located natural in the earth crust. Since biogas is classified as a renewable fuel, it can replace the use of fossil fuels. (Svensk Biogas 2010a) Biogas is a methane rich gas that consists of 55‐75% of methane, 30‐45% of carbon dioxide and 1‐2% of hydrogen sulphide. (Hilkiah et al. 2008) The biogas generation can be divided into two different processes according to their temperature; mesophilic (14‐40° C) and thermophilic (40‐60° C). The mesophilic processes is slower than the thermophilic, but instead it is more stable and not as sensitive to changes in the surrounding environment. (Nationalencyklopedin 2010d)3.7.1 Production
The process of producing biogas can include the following steps: Firstly, the incoming organic material is dispersed in a large tank. After this, the material is heated up to a temperature of 70 °C during at least one hour. This process takes place in order to eliminate the bacteria in the waste. Next, the waste is cooled down and after this the material enters the digestion chamber. In the digestion chamber the temperature is approximately 38 °C, the process is anaerobic (no oxygen is present) and material will be located here during a period of approximately 30 days. When the digestion process is over, the biogas that has been produced has a methane gas content of approximately 65%, the carbon dioxide content is roughly 35%. If the gas is to be used as vehicle fuel it is upgraded and the carbon dioxide is removed so that the methane content is around 97%. Depending on the material input for the digestion process, there is a possibility to produce bio sludge. The bio sludge can favorably be used as fertilizer. The process of producing biogas is displayed in Figure 3‐5. (Svensk Biogas 2010b) Figure 3‐5 – The biogas production steps (Svensk Biogas 2010b) Dispersing of organic material Heating step to remove bacteria Cooling Digestion Washing to remove CO2 97% methane gas for e.g. vehicle fuel Combustion of biogas
For the digestion process to be optimal the temperature should be kept constant and the pH‐value is supposed to be little over 7. During an anaerobic biogas digestion process, heat has to be added. This can be compared with aerobic digestion (i.e. composting) where a lot of heat is produced.
(Bioenergiportalen 2008) 3.7.2 Combustion of Biogas
To be able to incinerate the biogas that has been produced, the gas firstly has to be dried. It also has to be cleaned from corrosive materials and particles. After this, the gas is combusted in a gasturbine (for larger production scale) or in an engine (for smaller production scale). The efficiency of the electricity generation from combustion of biogas is normally around 30‐40% (depending on the efficiency in the turbine/engine). The heat produced through the combustion can also be utilized if heat recovery is used. (Biogasportalen 2009a)
3.7.3 Biogas in Sweden
The total biogas production was approximately 1400 GWh during 2008 in Sweden, which was a 12% increase since 2006. The biggest part of the production is in wastewater treatment plants, but there are also production from landfills and industrial facilities. (Biogasportalen 2008) In the south of Sweden, there is a natural gas grid supplying several big cities and at some places, biogas is fed into this gas grid, replacing natural gas. (Energigas Sverige 2010) The biogas can also be used as vehicle fuel and it is considered a cleaner fuel compared to both diesel and gasoline. (Svensk Biogas 2010c)
3.8 Environmental Aspects of Waste Management Techniques
Regardless of the type of waste management, there are benefits and draw backs to all of them. Whether the benefits and drawbacks are economical, political or environmental the different treatment methods have to be evaluated.
3.8.1 Landfilling and Open Dumping
As mentioned earlier in 3.5, one of the most common ways to treat waste is by landfills or open dumps. On an organized landfill, the waste is covered with soil and other material such as mining waste, which also decrease the volume of the waste. When covering the waste, this prevents settings. Today, there are a large number of open dumps in the world, especially in developing countries. This is mainly due to the small costs in disposing the waste instead of treating it. When not covering the waste or decreasing the volume of it, landsliding is a common risk. (Avfall Sverige 2009d) In both landfills and open dumps, the different materials take long time to digest. At most landfills and dumps, methane gas generation, as well as carbon dioxide generation, occurs naturally from the organic waste. When organic waste is digested with oxygen, carbon dioxide is generated, while digestion of organic material without oxygen present generates methane gas. Both these are greenhouse gases. (ÅF Energi och Miljöfakta 2010d) The GHG generation can continue a long time even after the waste has been landfilled. (Avfall Sverige 2009d) When using landfills or especially open dumps, there are risks of landfills fires. These fires can occur when the organic waste is decomposing and therefore producing heat that can ignite. There are great risks with these fires. The waste contains several different materials and the emissions from the fires can be hazardous. (Naturvårdsverket 2009c)
Even today, not everything is known about the effects regarding the emissions from landfills and open dumps. The waste materials at open dumps and landfills can affect the ground water due to stormwater. The main emissions from the stormwater are nitrogen, oxygen consuming subjects, metals and organic environmental toxins such as dioxins. (Naturvårdsverket 2008) The effects from the stormwater can however somewhat be controlled by using physical barriers and regularly controls. (ÅF Energi och Miljöfakta 2010d) There are several heavy metals involved at open dumps and landfills. An investigation including tests on samples from the Thai Nonthaburi dumpsite showed that the three most common heavy metals in the waste were zinc, copper and manganese. (Prechthai, Parkpian & Visvanathan 2008) Prechthai, Parkpian & Visvanathan (2008) also conclude that it is necessary to focus on removing heavy metals from the leachate.
3.8.2 Waste Incineration
When incinerating waste in facilities with flue gas purification systems, the emissions are controlled and the dioxin emissions are much smaller than from landfills. (ÅF Energi och Miljöfakta 2010a) Since 1980’s, the dioxin emissions from waste incineration has decreased with 99% and today the emissions to air from waste incineration is about 0.8 g/year. (Naturvårdsverket 2009d) When using waste incineration, the volume of the waste is also decreased, normally by 90‐95%. (ÅF Energi och Miljöfakta 2010a) In the chimney gases from the waste incineration, several heavy metals are involved, e.g. mercury, zinc and cadmium. There are other non‐organic materials such as hydrogen chloride and hydrochloric acid in the gases as well. Today, all Swedish waste incineration stations are supplied with effective cleaning system to decrease the emissions. Due to this, the total amount of emissions from the waste incineration has decreased although the incineration has increased. (ÅF Energi och Miljöfakta 2010f) Most ashes from biofuels contain important minerals and nutrients and it is therefore important to restore the ashes to the forest. All biofuels contain metals since plants absorb metals from the ground. Most of these metals stay in the ashes after incineration and are therefore a risk for ecosystems when the ash is restored to the forest. (ÅF Energi och Miljöfakta 2010g)
Waste incineration is not a step against reducing the production of waste. Instead, it is by some, considered as a shortcut for minimizing the waste and that it acts like a barrier, neglecting recycling. (Greenpeace 2005) There are also some concerns regarding the possibility of developing cancer from the chimney gases. (BBC NEWS 2010)
3.8.3 Biogas
Biogas can be considered as waste‐to‐energy since the organic part of the municipal solid waste is used as feedstock for the production. This leads to reduced waste volumes on landfills. Biogas does not contain as many particles as fossil fuels. (Svensk Biogas 2010c)
Methane is about 23 times stronger as a GHG, compared to carbon dioxide. The methane transforms into carbon dioxide during combustion. (EPA 2010) The carbon dioxide that is generated when the biogas is incinerated does not affect the climate changes, it is said to be carbon dioxide neutral. (Biogasportalen 2009b) This means that there is no net contribution of carbon dioxide to the atmosphere. When carbon dioxide is released by combustion, this is later added to the plants in the photosynthesis, resulting in growth of new biomass. (Nationalencyklopedin 2010e)
The fertilizer from the biogas production is of high quality. The nutrients are not lost in the process since the digestion process takes place in closed facilities. When using the fertilizer from the biogas production, this reduces the need for commercial fertilizers. (Svensk Biogas 2010c) As mentioned with waste incineration, biogas production from MSW also has a drawback regarding the fact that it does not prevent the waste generation.
3.9 District Heating and Cooling
District cooling as well as district heating, are ways to supply heating or cooling. As the name indicates the production of heating or cooling does not take place at the same location as it is used. Instead of using smaller heat or cold producing machines, the production is centralized. Environmental benefits are achieved since it is more efficient to produce heating and/or cooling at one bigger and better adapted facility, instead of at several smaller ones. There are advantages of a more practical nature for the end users as well: there is no noise, no dripping and no maintenance is required. The use of district cooling frees spaces as well. (Svensk Fjärrvärme 2005b) The first district heating system in the world started running in USA in 1877. This system was based on distribution of steam. In Europe it took until 1900 before the first district heating system was built in Germany. At present, district heating exists in most countries where there is a need for heat. (Werner & Fredriksen 1993)
The district cooling systems appeared later than the district heating systems. One of the first district cooling systems was taken into operation in 1962 in USA, while the first to use it in Europe were the French, in 1967. The first Swedish system was in place in 1992 in Västerås. (Svensk Fjärrvärme 2002) In Sweden, district heating is more common than district cooling. District heating provides approximatley half of the heated buildings and premises in Sweden. However, the need for district cooling is also growing. This increased demand is believed to be a result of higher demands of indoor comfort, as well as the prohibition of some of the most common refrigerants. Nevertheless, the world’s energy usage for producing cold is greater than the usage for producing heat. (Svensk Fjärrvärme 2005a) & (Svensk Fjärrvärme 2005b)
For both district heating and district cooling, water is often used to transport the heating or cooling. The transportation is via pipelines. (Svensk Fjärrvärme 2005a) District heating can however also be hot steam, delivered to for instance industries that use steam in their processes. (Svensk Fjärrvärme 2003) District cooling recipients can be residential buildings, hospitals, industries, offices etcetera. The cooled water that is distributed is used to chill the air that is circulating in the room. The water is returned to the production facilities afterwards to be cooled once again. (Svensk Fjärrvärme 2005a) Cooling of the water for district cooling can be achieved in three different ways: • Free cooling • Absorption cooling • Compression cooling If free cooling is used, this means that naturally cold sources are used, such as water from lakes or rivers. Absorption cooling is a technique that is powered by heat. The heat can be hot water or
steam, a common alternative in Sweden is to use hot water from a district heating system. Compression cooling uses electricity as source of energy. (Svensk Fjärrvärme 2005a)
Regarding heating, district heating gives the user more freedom compared to having a boiler and being dependent on one single source of energy. (Svensk Fjärrvärme 2009)
3.10 Compression Cooling
The second law of thermodynamics state that heat cannot by itself move from a body or location with low temperature, to a body or location with high temperature. So to achieve cooling, power of some kind is needed, which can be high temperature heat or electrical energy. (Nationalencyklopedin 2010f) To refrigerate is by definition “the process of removing heat from an enclosed space or from a substance for the purpose of lowering the temperature”. In other words, the goal is to achieve a lower temperature than that of the surrounding environment. (Encyclopædia Britannica 2010a)
A compressor‐driven cooling machine (CCM) normally refers to the use of the vapor‐compression refrigeration cycle. This is the most commonly used working cycle for cooling facilities. The same cycle is used for heat pumps, but when heat is desired the warm side (the condenser) is used instead of the cold side (the evaporator). The vapor‐compression refrigeration cycle is a closed system in which a refrigerant (the working medium) circulates. The refrigerant is alternating between liquid and gas form in the four steps of the cycle:
• The compressor in which the refrigerant is compressed isentropically (constant entropy) from saturated vapor to superheated vapor. The refrigerant has a temperature high above the surrounding temperature.
• The condenser, where the refrigerant releases heat to the surroundings and transforms into saturated liquid. The temperature of the refrigerant is still higher than the surrounding temperature.
• The expansion valve, where the pressure drops and therefore also the temperature of the refrigerant, which is now lower than the temperature of the surrounding environment. • The evaporator, in which the refrigerant evaporates by absorbing heat from the cooled
space. The refrigerant enters as a saturated mixture and leaves as saturated vapor.
After the evaporator the refrigerant enters the compressor again, and the cycle is complete. (Cengel & Turner 2004)
Common refrigerants that have been used for long times are called CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). These are being phased out however, since the chlorine depletes Earth's stratospheric ozone layer. (Access Science 2010b) For industrial applications, ammonia and Freon‐22 are the most commonly used refrigerants. Freon‐11 and Freon‐12 are mostly used in air conditioning units. Freon was more common earlier in e.g. refrigerators, but today it is forbidden to apply in new systems. (Nationalencyklopedin 2010g) In refrigerant systems, ammonia is commonly used due to its high vaporization heat. Ammonia is hazardous and poison in larger volumes. (Nationalencyklopedin 2010h)
3.11 Absorption Cooling
Absorption cooling has become more popular lately but the technique is actually quite old. Already during the 19th century patents were granted and around 150 years ago the development started. (Rydstrand, Martin & Westermark 2004)
The absorption chilling machine (ACM) works according to the same principle as the compression cooling machine, but with some alternations. The essential difference is that instead of an electrical compressor, absorption cooling utilizes a generator and an absorber, i.e. a thermal compressor. (Energy Solutions Center 2010)
The other big difference is that the absorption cooling process uses two working mediums for the process, a refrigerant combined with an absorbent. Normal working medium combinations are lithium bromide/water or water/ammonia. In the lithium bromide combination the lithium bromide works as absorbent and the water as refrigerant while in water/ammonia solution, the water is the absorbent and the ammonia is the refrigerant. The absorption cooling process consists of the following steps (here with the example of lithium bromide/water as working couple): (Zinko et al. 2004)
• The absorber, in which water steam from the evaporator and concentrated absorbent, lithium bromide, are mixed. The lithium bromide absorbs the steam and a low pressure is achieved. This also releases heat that needs to be cooled off to maintain the low pressure. When the lithium bromide cannot absorb any more water, it is pumped to:
• The generator, where heat in some form is added, which vaporizes the water, and therefore the lithium bromide and the water are separated again. On its way to the generator, the solution also passes a heat‐exchanger, in order to decrease the amount of heat that needs to be added in the generator. The separated absorbent is fed via the heat exchanger as well as an expansion valve, back to the absorber. The water steam, on the other hand, is fed to: • The condenser, where heat is removed from the vaporized refrigerant and condenses. The condensed refrigerant is afterwards passed on via an expansion valve, to: • The evaporator, where the pressure and temperature is low enough for the refrigerant to vaporize through absorbing heat from the cooled space. This is where the actual desired cooling occurs. The water, in the form of steam, is passed on to the absorber and the cycle is complete.
(Zinko et al. 2004)
Figure 3‐6 ‐ Schedule displaying compression cooling and absorption cooling (adapted from Martin, Setterwall & Andersson 2005) 3.11.1 Distribution When using absorption cooling to satisfy a cooling demand this can be done in different ways. One option is to have the ACM placed at the premises of the heat producing company, and the cold water is distributed to the customer from there. This is district cooling. The other alternative is that the absorption cooling machine is placed closer to the customer, and the hot water is delivered there through district heating pipes. The cold water is afterwards transported from there to the customer. This alternative is referred to as district heat driven cooling machine. District heat driven cooling machines are suitable when there is an existing district heating system, which is the case in e.g. Sweden. District cooling is more common the USA and Japan while district heat driven cooling machines occurs more in Europe. (Rydstrand, Martin & Westermark 2004)
3.11.2 The Absorption Cooling Machine
There are a number of different absorption cooling machines that require driving temperatures within certain intervals and they also provide different efficiencies. Here, the conventional single‐ and double‐effect will be presented, as well as the low temperature driven semi‐effect ACM. The conventional absorption cooling machines require a heat source with temperatures from 120°C for a single‐effect (SE) ACM up to 170°C for a double effect (DE) ACM. The efficiency of the energy use for the absorption chiller can be calculated as the relation between the cooling effect of the cold water and the added driving effect. This relation is called the Coefficient of Performance (COP). The COP of a single‐step water/lithium bromide absorption cooling machine is approximately 0.7 or 0.8, while for a double‐effect the COP can be 1.2. The main application of the conventional ACMs is to place them next to e.g. production facilities where waste heat of high temperature is available. If
these conventional ACM are used with district heating as heat source, this gives a lower COP due to lower temperature of the district heating. (Zinko et al. 2004)
The SE ACM works in two different pressure levels, while the DE ACM works in three different pressure levels. The SE‐machine has a high pressure level in the generator and condenser, and a low pressure level in the evaporator and absorber. For the DE‐machine an additional pressure level is added, named a high‐pressure generator and a high‐pressure condenser. The heat that is emitted in the high‐pressure condenser can be reused in the low‐pressure generator. The result is that more heat can be absorbed in the evaporator with the same amount of added heat. Due to the three pressure levels in a double‐effect machine this is more advanced than a single‐effect one since more pumps and heat‐exchangers are needed. On the other hand, if a cooling tower is needed as a heat sink, the installed cooling tower capacity per cooling effect is less for a double‐effect ACM than for single‐effect. This brings the price level of the DE‐ACM closer to the SE‐ACM, although the DE is normally more expensive. (Rydstrand, Martin & Westermark 2004) There are ACMs that can be powered by low temperature heat (70‐90°C), for example district heat water. This ACM is called a semi‐step (SS) ACM. The principle for this is the same as the DE‐ACM but without the internal heat exchange. The SS‐ACM has two generators, two absorbers, one condenser and one evaporator. The two generators is the reason to why driving heat within a larger interval can be used. As a result of this, larger heat exchange areas are needed, and possibly more pumps, which increases the price of the machine. The expected COP for a machine like this is 0,7. The interest for the low temperature heat driven ACM has increased in many parts of the world where there is access to low temperature heat like solar heat, earth heat, heat from CHP production or from waste incineration. (Rydstrand, Martin & Westermark 2004) The estimated characteristics for the three mentioned ACMs can be viewed in Table 3‐1 below.
Table 3‐1 – Estimated characteristics for different ACMs (Rydstrand, Martin, Westermark 2004)
Type of ACM COPelectricity Required temperature [°C]
Single Effect (SE) 0.7 120 Double Effect (DE) 1.2 150‐170 Semi Step (SS) 0.7 > 65 The investment cost for an ACM is higher than for a CCM. However, the overall cost for the ACM can be decreased by at least 50% by placing the absorption cooling nearby a natural heat sink, e.g. a lake. This is compared to the alternative where cooling towers are needed. (Martin, Setterwall & Andersson 2005) According to Zinko et al. (2004) the cooling effect and thereby the investment cost is a function of the temperature of the heat used in the ACM. Zinko et al. (2004) also states that it is a matter of a system optimization with the parameters heat, cooling and electrical power, and the price differences among these.
For the ACM to be economically profitable, there has to be a thermodynamic difference, a factor between the electricity price and the heat price of about 2.5‐3. The biggest usage possibility can be found when the driving heat originates from facilities with waste heat or from CHP plants where the heat is considered as a byproduct from the electricity production. (Zinko et al. 2004)
3.12 Efficiency of ACM Compared to CCM
As mentioned before the single‐effect ACM has a COP of approximately 0.8. The COP for a CCM is higher, as high as 4.5 for a large scale water cooled chillers, while 2‐4 is common in Europe for smaller CCMs. The COP value for the ACM is however based on heat as power source, while for the CCM the value is based on electricity as source of power. Due do this, absorption cooling is often considered to be an inefficient way to produce cooling. Rydstrand, Martin & Westermark (2004) explains why this is approach is inaccurate. The efficiency of a thermodynamic process can be valued with an ideal Carnot‐process as a reference. What Rydstrand, Martin & Westermark (2004) refers to as the Carnot‐factor is the efficiency of a process, divided by the efficiency of a Carnot‐process working with the same internal temperatures. (Rydstrand, Martin & Westermark 2004)
The Carnot‐factor does, per definition, equal one for an ideal process. For expansion in a steam turbine the Carnot‐factor is normally between 0.5 and 0.7, where 0.7 is for a very large steam turbine (e.g. condense power plant) and 0.5 for an average sized CHP plant. For a compressor driven cooling machine the Carnot‐factor is also around 0.5‐0.7 depending on size and efficiency. Consequently, the Carnot‐factor for producing cooling with a compression cooling machine that is run of electricity from a steam turbine, the total Carnot‐factor is 0.25‐0.5. Regarding an absorption cooling machine, the Carnot‐factor is 0.7 when no consideration is taken to external heat transfer. The conclusion is that cooling produced with an ACM is a thermodynamic shortcut compared to first generating electricity in a steam turbine and afterwards using the electricity to produce cooling with a CCM. The Carnot‐factor for absorption cooling is in comparison approximately twice as big as for compression cooling. Figure 3‐7 shows this comparison. (Rydstrand, Martin & Westermark 2004)
