This study presents the environmental impact assessment of an absorption heat transformer designed to recover 1 kW of thermal energy from each 2 kW of waste heat supplies. The net contribution of the heat transformer is a load avoided of 0.665 kg CO2 equivalents; the recovery process avoids 0.729 kg CO2 equivalents and the major contribution to the environment impacts is the pumping process with 0.0437 kg CO2 equivalents for each 1 kWh recovered. The study results show that absorption heat transformer is a good environmental option because it produces useful energy from waste heat and the final result is an environmental impact diminution.
The electricity consumption by the industry is 42.3% which is equivalent to 709 Mtoe (million tonnes of oil equivalent) [
A heat transformer is a device which can deliver heat a higher temperature than the temperature of the fluid which is fed, normally waste heat energy from industrial processes or renewable energy such as solar or geothermal energy [
Energy recovery is an important topic in industries where high amounts of heat are wasted. Many industrial processes require large amounts of steam or hot water to heat the process streams.
Absorption heat transformers (AHTs) are thermo-mechanical devices in which the main feature is the recovery of waste heat. AHTs are capable of recovering a large amount of energy and increase its temperature, using part of the same energy as power in a thermodynamic cycle. The increased temperature inside any closed thermodynamic system is a consequence of the increment of pressure. The difference of pressure in an AHT is obtained by means of a relatively small amount of mechanical energy supplied by a mechanical pump to move a fluid [
Large quantities of heat from industries have been rejected to the atmosphere, which not only wastes energy but also pollutes the environment [
As a very effective device, the AHT can be applied to improve low-grade waste heat with temperatures ranging from 60˚C to 100˚C. The AHT system can effectively recover about 50% of this waste heat and give an opportunity to reuse it in industrial processes [
The European Commission presented the Life Cycle Assessment (LCA) as an important framework for evaluating the environmental impact of products, processes or systems [
LCA quantifies energy, materials and wastes released to the environment and performs the impact assessment of those inputs and outputs. The application of LCA follows a standardized procedure described in ISO 14040: 2006 [
LCA studies help to avoid resolving one environmental problem while creating others: this unwanted “shifting of burdens” is where you reduce the environmental impact at one point in the life cycle, only to increase it at another point. Therefore, LCA helps to avoid, for example, causing waste-related issues while improving production technologies, increasing land use or acid rain while reducing greenhouse gases, or increasing emissions in one country while reducing them in another. Life Cycle Assessment is therefore a vital and powerful decision support tool, complementing other methods, which are equally necessary to help effectively and efficiently make consumption and production more sustainable [
Many theoretical and experimental studies of AHT have been carried out [
The AHT system consists basically of five plate heat exchangers (generator, condenser, evaporator, recovery and absorber), piping and accessories, two pumps and Lithium Bromide (LiBr) solution as a working fluid.
A constant heat waste is supply to the generator in order to vaporize a part of the working fluid (water) to the aqueous LiBr solution at low pressure. The vaporized working fluid flows to the condenser, delivering an amount of heat at close ambient temperature. The liquid leaving the condenser is pumped, to the evaporator at a higher-pressure zone. The working fluid is then evaporated at high pressure into the evaporator using a second quantity of heat waste at an intermediate temperature. At same time, the vaporized working fluid goes to the absorber, inside of which, it is absorbed by the concentrated in absorbent solution; this stream comes from the generator. The absorption process delivers useful heat at higher temperature.
The increased awareness of the importance of environmental protection, and the possible impacts associated with products (including services), both manufactured and consumed, has increased interest in the development of methods to better understand and address these impacts. One of the techniques used for this purpose is LCA [
1) the goal and scope definition phase.
2) the Life Cycle Inventory analysis phase (LCI phase), it is an inventory of input/output data with regard to the system being studied. It involves collection of the data necessary to meet the goals of the defined study.
3) The Life Cycle Impact Assessment phase (LCIA) is the third phase of the LCA. The purpose of LCIA is to provide additional information to help assess a product system’s LCI results so as to better understand their environmental significance. LCIA phase aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product. The method use for this study is IPCC 2007 which is a method developed by the International Panel on Climate Change. This method lists the climate change factors of IPCC with a timeframe of 20, 100 and 500 years [
4) Life cycle interpretation is the final phase of the LCA procedure, in which the results of an LCI or an LCIA, or both, are summarized and discussed as a basis for conclusions, recommendations and decision-making in accordance with the goal and scope definition.
The Goal: The purpose of this study is assessment the environmental load of an absorption heat transformer. The intended application is to identify environmental improvements opportunities in the process involved.
The scope: The product system is an absorption heat transformer which recovers heat waste from an external source in the evaporator and generator.
The system boundary: Four processes are considered in this study (assembly, recovery, pumping and LiBr (Lithium Bromide) solution) and shown in
Allocation: there is not process shared with other products.
Functional Unit: The functional unit is 1 kWh recovered for the system.
Data quality requirements: the data for assembly process were taken directly from the equipment and the data for all the other process were obtained from SimaPro software [
Assumptions:
・ No energy loss in the system.
・ The recovered energy is considered as electrical energy avoided.
・ Assembly, lifetime: 40,000 hours.
・ LiBr Solution, lifetime: 1000 hours.
The Heat Transformer processes are: assembly, recovery, pumping and LiBr (Lithium Bromide) solution.
Tables 1-4 show the material list and input/output energy for each process.
Material | Quantity | Unit |
---|---|---|
Steel, low-alloyed | 90.538 | kg |
Steel, chromium steel18/8 | 11.343 | kg |
Elastomere (Tube insulation) | 0.260 | kg |
Tetrafluoroethylene | 0.402 | kg |
Vinyl fluoride | 0.402 | kg |
Nylon 6-6 | 0.038 | kg |
Cable | 0.070 | kg |
Copper | 0.200 | kg |
Material | Quantity | Unit |
---|---|---|
Ethylene glycol | 0.3324 | kg |
Lithium hydroxide | 0.4125 | kg |
Bromine | 1.3935 | kg |
Tap water | 1.2187 | kg |
Process | Quantity | Unit |
---|---|---|
Generator | −1 | kWh |
Condenser | +1 | kWh |
Evaporator | −1 | kWh |
Recovery | −1 | kWh |
Note: The net contribution of energy of the system is in the Recovery Process. The negative value means that electrical energy (kWh) is avoided.
Process | Quantity | Unit |
---|---|---|
Pumping 1 | 0.030 | kWh |
Pumping 2 | 0.030 | kWh |
Life cycle impact assessment phase (LCIA), aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product [
The Substances i for climate change category are shown in
In this phase the environmental effects of each process (assembly, recovery, pumping and LiBr solution reaction) are quantified and evaluated for the impact category Climate Change considered in this study, the impact is expressed in a common unit (kg CO2 equivalents)/(kg of Substance). The SIMAPRO software [
The negative values means the quantity avoided; as an example, in the heat transformer, the substance carbon dioxide from fossil fuel (−621.8310824 g) means than this quantity is avoided. In the assembly process the substance carbon dioxide from fossil fuel (5.596467 g) means than this quantity is emitted to environment.
The AHT system net contribution is an emission avoided of 0.665 kg CO2 eq (see
Substance | Unit | Heat Transformer | Assembly | Pumping | Solution LiBr | Recovery |
---|---|---|---|---|---|---|
Methane, chlorodifluoro-, HCFC-22 | mg | 0.9930 | 1.0007 | 0.00051 | 0.0002308 | −0.008433 |
Methane, trifluoro-, HFC-23 | μg | 63.746 | 63.766 | 0.00140 | 0.0021461 | −0.023326 |
Sulfur hexafluoride | μg | −144.638329 | 0.193051 | 9.27570 | 0.4879222 | −154.5950 |
Methane, fossil | mg | −826.836511 | 17.58988 | 55.55473 | 25.9310568 | −925.9122 |
Dinitrogen monoxide | mg | −75.2300337 | 0.150714 | 4.844296 | 0.51322689 | −80.73827 |
Carbon dioxide, fossil | g | −621.830824 | 5.596467 | 40.65573 | 9.51253638 | −677.5956 |
# | Sustance | Factor | Unit |
---|---|---|---|
1 | Methane, chlorodifluoro-, HCFC-22 | 1810 | kg CO2 eq kg |
2 | Methane, trifluoro-, HFC-23 | 14800 | kg CO2 eq/kg |
3 | Sulfur hexafluoride | 22800 | kg CO2 eq/kg |
4 | Methane, fossil | 25 | kg CO2 eq/kg |
5 | Dinitrogen monoxide | 298 | kg CO2 eq/kg |
6 | Carbon dioxide, fossil | 1 | kg CO2 eq/kg |
Substance | Unit | Heat Transformer | Assembly | Pumping | Solution LiBr | Recovery |
---|---|---|---|---|---|---|
Total | kg CO2 eq | −0.6652 | 0.00929 | 0.043715 | 0.01035 | −0.72859 |
Other substances | kg CO2 eq | 0.00024 | 0.00045 | 1.47E−05 | 2.04E−05 | −0.00025 |
Methane, chlorodifluoro-, HCFC-22 | kg CO2 eq | 0.00180 | 0.00181 | 9.2E−07 | 4.2E−07 | −1.53E−05 |
Methane, trifluoro-, HFC-23 | kg CO2 eq | 0.00094 | 0.00094 | 2.07E−08 | 3.12E−08 | −3.45E−07 |
Sulfur hexafluoride | kg CO2 eq | −0.0033 | 4.40E−06 | 0.000211 | 1.11E−05 | −0.00352 |
Methane, fossil | kg CO2 eq | −0.0207 | 0.00044 | 0.001389 | 0.000648 | −0.02315 |
Dinitrogen monoxide | kg CO2 eq | −0.0224 | 4.49E−05 | 0.00144 | 0.00015 | −0.02406 |
The pumping process is the highest contributor to the environmental load (see
The efficient use of energy and minimum environmental impact of chemical processes are an important task today. By means of energy recovery systems, it is possible to improve the energy efficiency and the life cycle assessment is possible to evaluate the environmental impact of chemical processes. In the present work, the life cycle assessment of an absorption heat transformer which is designed to recover 1 kWh of heat in 1 hour from each 2 kWh of waste heat supplies in the generator and evaporator equipment was performed.
The life cycle assessment of the Absorption Heat Transformer shows that the substance with major emission is from carbon dioxide fossil to air. The net contribution of heat transformer is an emission avoided of 665 g CO2 eq. and the recovery process avoids 728.6 g CO2 eq. and the major contribution to the environment impacts is the pumping process 43.7 g CO2 eq. The pumping process is the main contribute to the environment impact emitted. This process uses a source of electrical energy that can be replaced with solar energy.
The environmental impact assessment of this Absorption Heat Transformer has shown that this technology can be a good option to recover waste energy in a sustainable way.
Authors thank to CB-167434 CONACYT project.
Jorge Avelino Domínguez Patiño,Antonio Rodríguez Martínez,Rosenberg Javier Romero,Jonathan Ibarra-Bahena,Martha Lilia Domínguez Patiño, (2016) Environmental Impact Assessment for an Absorption Heat Transformer. Open Journal of Applied Sciences,06,409-415. doi: 10.4236/ojapps.2016.67042