Life Cycle Assessment of improved high pressure alkaline electroly PDF
Preview Life Cycle Assessment of improved high pressure alkaline electroly
Life Cycle Assessment of improved high pressure alkaline electroly‐ sis Jan Christian Koj1, Andrea Schreiber1, Petra Zapp1, Pablo Marcuello2 1) Forschungszentrum Jülich, Institute of Energy and Climate Research ‐ Systems Analysis and Technology Evaluation (IEK‐STE), D‐52425 Jülich, Germany 2) Fundacion para el Desarrollo de Nuevas Tecnologias del Hidrogeno en Aragon (FHa), E‐22197, Spain Executive Summary This report investigates environmental impacts of high pressure alkaline water electrolysis systems. Advanced systems with new improved membrane technology are compared to a state‐of‐the‐art system with asbestos membranes using a Life Cycle Assessment (LCA) ap‐ proach. This LCA is compliant to ILCD [JRC, 2011] and therefore also to ISO 14040 [International Organization for Standardization (ISO), 2006a], 14044 [International Organization for Standardization (ISO), 2006b] and FC‐HyGuide [Lozanovski, 2011]. Most of the relevant data derive from the partners in the EU research project “ELYGRID”. Results indicate that most environmental impacts are caused by the electricity supply necessary for operation. During the construction phase cell stacks are the main contributor to environ‐ mental impacts. Membranes have relatively small contributions to impacts caused by cell construction within the considered systems. As main outcome the systems comparison illus‐ trates a better ecological performance of the new improved system. Keywords Life Cycle Assessment, hydrogen production, alkaline water electrolysis, environmental im‐ pacts Contribution to ELYGRID project 2 I Introduction The inherent variability of renewable energy sources causes risks for the reliability of electri‐ cal power grids. Therefore, balancing variable renewable energy (VRE) is increasingly recog‐ nised as a serious, worldwide challenge [Droste‐Franke et al., 2012]. These developments led to a renewed interest in hydrogen production technologies. Outstanding characteristics, e.g. flexibility and high efficient hydrogen production from renewable electricity resources, make water electrolysis a good candidate for future low‐carbon hydrogen production. Alkaline water electrolysis is a mature hydrogen production technology. However, the state of this technology did not improve significantly within the last decades. Asbestos has been extensively used as membrane material for many years and is still widely in use in existing electrolysis systems. Nonetheless, regulation (EC) No 1907/2006 (also known as REACH) [European Union, 2006] started a new development. It prohibits to put asbestos on the mar‐ ket as well as the supply and use of asbestos fibres of all types and of products containing asbestos fibres. Hence, for new alkaline electrolysis systems the use of asbestos membranes is not allowed any more, new membranes are necessary for hydrogen generation. Within the “ELYGRID” project improved non‐asbestos membrane materials for novel electrolysis systems are investigated. The purpose of the current study is to present an in‐depth assessment of environmental im‐ pacts induced by these advanced alkaline water electrolysis systems in comparison to state‐ of‐the‐art asbestos systems. Environmental assessments of hydrogen production have been subject in many studies. However, a review paper shows that most of these studies had an exclusive focus on Global Warming Potential (GWP) [Bhandari et al., 2014]. Little attention has been paid to evaluation of ecological effects of individual alkaline electrolysis constitu‐ ents. Therefore, modeling of environmental impacts caused by an exchange of membranes was not possible in the past. The “ELYGRID” project provides a great opportunity for a de‐ tailed environmental assessment of advanced asbestos‐free membrane materials and entire alkaline water electrolysis systems. Life Cycle Assessment (LCA) is used as method for environmental assessment within this study. LCA involves environmental impacts over the entire lifetime of products or systems. Finally, the main aim of this report is to present key results of the LCA and to answer the question if the technological advancement of electrolysis systems leads to environmental improvement. I.1 Analysed systems The LCA includes a comparative presentation of the environmental outcomes of three dif‐ ferent electrolysis systems. A state‐of‐the‐art asbestos electrolysis system is compared to advanced non‐asbestos systems. Reference is a state‐of‐the‐art 3.5 MW electrolysis system using conventional asbestos membranes (system I). The second system (II) includes the ad‐ vanced polymer based membrane instead of the asbestos membrane. This system is as‐ 3 sessed to evaluate the effects of changes on cell level solely. In addition, an advanced sys‐ tem, which is planned for commercial operation, including further Balance of Plant (BOP) improvement (redesign of mechanical components, infrastructure changes) is analyzed (sys‐ tem III). These changes concern optimized gas separators and heat exchangers as well as some pumps with enhanced power demand. The system power of 6 MW is planned for the advanced systems. These systems, using advanced membranes, achieve higher hydrogen outputs with the same number and diameters of cells. Essential technical parameters are summarized in Tab. 1. Tab. 1: Technical characteristics of compared electrolysis systems Conventional Advanced System System without BOP BOP improve‐ improvement ment I II III System power MW 3.5 6.0 Hydrogen output kg/hr 68 116 Electricity consumption kWh /kg H 57.3 53.9 el 2 Cells per stack pcs 139 Stacks pcs 4 Cell diameter m 1.6 Operating pressure bar 33 Operating temperature °C 85 Volume of gas separator l 10 5 Power of KOH cycle pump kW 1.5 3 Power of de‐ion. water kW 10 20 pump Heat exchanger weight kg 22,000 3,891 Source: IEK‐STE 2015 IEK‐STE 2015 Within the assessment of these systems specific conditions of the ELYGRID project are con‐ sidered. Country‐specific operating conditions in Spain like the average electricity grid mix or 4 Spanish wind power mix are considered. Furthermore, specific transports of the system components are construction the manufacturing of components and their transportation to the northern part of Spain, where the electrolysis tests of the ELYGRID project take place, are involved in the calculations (e.g. transport of cell stacks from Switzerland to Spain). I.2 System components The following paragraphs give an overview of system components. Central components of the systems are the cell stacks, where the electrolysis takes place. The number and diameter of cells of all three systems is the same. Electroylsis cells inside the stacks are constructed in a “sandwich” formation. The membrane is embedded between the anode and cathode. Furthermore, each cell also contains a gasket and cell frame. The cell stack assembly requires processed steel and copper. Moreover, there are further components necessary for the system assembly and operation: • Gas separator (for separating O and H ) 2 2 • Lye tank for potassium hydroxide (KOH) • KOH filter • Heat exchangers (for cooling of O , H , and KOH) 2 2 • Pumps (pumping of KOH and water) • Power electronics There are various flows between these systems components. Fig. 1 shows these flows in a flow chart. 5 Fig. 1: Technical characteristics of compared electrolysis systems Source: FHa 2014, modifications by IEK‐STE 2014 IEK‐STE 2015 The flow chart can be applied on all three systems, due to their same basic structure. In two gas separators the disunite oxygen and hydrogen gas flows are cooled down and dehumidi‐ fied. The pink lines show the flows of KOH, which circulates in the systems. Furthermore, there is a second cycle within the system. Cooling water circulates within this cycle and is marked by the green lines. There is further application for deionized water. For conducting the electrolysis a continuous water supply is required. II Method Purpose of the assessment is the implementation of an ISO‐ and ILCD‐conform LCA to com‐ pare the environmental effects of state‐of‐the‐art asbestos electrolysis systems to advanced non‐asbestos systems. II.1 LCA basics Life Cycle Assessment (LCA) is an adequate method for a holistic evaluation of environmen‐ tal effects. It is well‐established, internationally acknowledged, and defined in the ISO stand‐ ards 14040 [International Organization for Standardization (ISO), 2006a] and 14044 [International Organization for Standardization (ISO), 2006b]. Within LCA environmental im‐ pacts along the whole life cycle of products are assessed, comprising processes from mining of raw materials, production and use to recycling and/or disposal. ILCD is based on the ISO standards. ILCD stands for an International Reference Life Cycle Data System, which contains recommendations for Life Cycle Impact Assessment in the European context [JRC, 2011]. 6 Corresponding to the ISO norms, a LCA is composed of four stages [Bhandari et al., 2013]: 1. Goal and scope definition: The goal definition defines the purpose of the analysis. Scope definition determines the functional unit to be analyzed and system bounda‐ ries regarding region and time frame and methods used for impact assessment. 2. Life Cycle Inventory Analysis (LCI): In the LCI relevant data about energy and material inputs, emissions, wastes, and other releases are collected and quantified. 3. Life Cycle Impact Assessment (LCIA): The compiled inputs and outputs are catego‐ rized and assigned to environmental effects, the so called impact categories. 4. Interpretation: This last LCA step summarizes the LCI and LCIA results and their quali‐ ty. Conclusions and recommendations are drawn. II.2 LCA application on the ELYGRID project All three systems within this assessment are compared on the basis of the functional unit. For our assessment the production of 1 kg H at 33 bar and 40 °C are considered as function‐ 2 al unit. A technical service life of 20 years is considered for all systems. FC Hy‐Guide [Lozanovski, 2011] proposes the subdivision of hydrogen production systems in construction, operation, and end of life. In Fig. 2 this subdivision is illustrated for the consid‐ ered conventional and advanced alkaline electrolysis systems. Fig. 2: System boundary and processes of alkaline electrolysis systems considered Source: IEK‐STE 2015 IEK‐STE 2015 Besides manufacturing of the electrolyzer components the construction includes the assem‐ bly of system and its transport. Steel, copper, and electrolysis cells are integrated into cell stacks. Concerning the construction the main difference of the systems is the membrane material. Moreover, there are additional improvements in the cell, like lower weights, for the advanced system cases. 7 With regard to operation the system power and the resulting amount of hydrogen output are the main differences of the compared electrolysis systems. Beside the actual electrolysis process operation includes the necessary electricity and deionized water supply, the cycles of potassium hydroxide (KOH) solution and cooling water. A KOH solution with a concentra‐ tion of 25 % is used. The KOH solution is disposed after 10 years and replaced by a new solu‐ tion. During this operation time the KOH solution can be circulated without conditioning. Additionally, deionized water is used for system operation. For the production of 1 kg hydro‐ gen the amount of 10.11 l deionized water is required. Oxygen is co‐generated to hydrogen in the electrolysis process. For the system no subsequent use of the oxygen is considered and it is emitted into the atmosphere. As agreed by the project consortium H purification, 2 compression, H storage, and gas holder are not considered as part of the system investigat‐ 2 ed in the project and therefore not included into the system boundaries of this analysis. Two different operation scenarios are analysed within this assessment. As ecological best case an operation with wind power is considered. On the other hand an operation with electricity grid mix is assessed as worst case. For both cases a nearly year‐round operation with only five short stops and start‐ups a year is assumed. The prospective real operation will probably have lower full‐load hours, but is not clearly quantifiable by now. The asbestos parts (membranes and gaskets) and steel components are considered for dis‐ posal. As the disposal modalities of the new improved membranes are not finally clear, this disposal is not considered. II.3 LCI application on the ELYGRID project Data for 1st order processes (operation) including the amount of KOH, deionized water or electricity are provided entirely by the project partners. Life Cycle information about these operation materials or energy (2nd order processes) are taken from LCA data bases (especial‐ ly ecoinvent 2.2 and GaBi 6.0). Data for 3rd order processes (infrastructure for surrounding system) are also taken mostly from the data bases. As some data are not available (e.g. pro‐ duction of the asbestos membrane) the information have to be developed using secondary literature (e.g. patents, company brochures). II.4 LCIA application on the ELYGRID project In the Life Cycle Impact Assessment (LCIA) the gathered and aggregated inputs and outputs of the entire systems are categorized and allocated to environmental impact categories. The choice of impact categories is based on the ILCD guidelines [JRC, 2011]. Following impact categories are recommended and assessed within this LCA: • Abiotic Resource Depletion Potential ‐ mineral (ADP elem. [kg Sb‐eqv.]) • Abiotic Resource Depletion Potential ‐ fossil (ADP fossil [MJ]) • Global Warming Potential (GWP [kg CO ‐eqv.]) 2 • Acidification Potential (AP [kg SO ‐eqv.) 2 8 • Ozone Depletion Potential (ODP [kg R11‐eqv.]) • Eutrophication Potential ‐ saltwater (EP sw [kg N‐eqv.]) • Eutrophication Potential ‐ fresh water (EP fw [kg P‐eqv.]) • Photochemical Ozone Creation Potential (POCP [kg NMVOC]) • Human Toxicity Potential ‐ carcinogen (HTP c [CTUh ]) c • Human Toxicity Potential ‐ non carcinogen (HTP nc [CTUh ]) nc • Ecotoxicity Potential (ETP [CTUe]) • Particulate Matter (PM [kg PM ‐eqv.]) 2.5 For carrying out LCA of hydrogen production the European Union has developed and rec‐ ommended a guideline (FC‐HyGuide) [Lozanovski, 2011], which is applied in most parts of this study. However, its use in LCIA about hydrogen production via electrolysis has not been observed yet. Hence, ILCD guideline [JRC, 2011] is applied in this study for LCIA because of the larger number of assessment categories and its broad international recognition. By selecting this range of ILCD proposed impact categories and conducting ILCD based calcu‐ lations, a broader view on environmental effects is achieved than other LCA about hydrogen production did before. Additionally, a more detailed look on the impact contribution of spe‐ cial components of electrolysis systems is a main purpose of this study. III Life Cycle Inventory In the LCI all material and energy in‐ and outputs for the entire system are calculated. Within the subsequent LCIA these Inputs and outputs are allocated to environmental effects (Chap‐ ter IV). III.1 LCI Data for construction In a first step material amounts used for production of single cells are shown in Tab. 2. 9 Tab. 2: Material composition of electrolysis cells Asbestos Cell Advanced Cell Material kg Material kg Total 7.5 Total 2.619 Chemicals for im‐ Chrysotile‐Asbestos 7 2.619 proved membranes Polyester resin 0.35 ‐ ‐ Membrane Dimethylformamide 0.102 ‐ ‐ Toluol 0.022 ‐ ‐ Styrol 0.006 ‐ ‐ Total 10.2 Total 10.2 Anode Nickel 10.2 Nickel 10.2 Total 10.2 Total 10.2 Nickel 9.53 Nickel 9.53 Cathode Aluminium 0.4 Aluminium 0.4 Carbon monoxide 0.26 Carbon monoxide 0.26 Total 55 Total 51 Cell frame Steel 45.8 Steel 43.4 Nickel 9.2 Nickel 7.6 Total 0.7 Total 0.7 Asbestos paper 0.621 Aramid fibres 0.105 Acrylonitrile‐ Gasket Tetrafluorethylene 0.0789 0.14 butadiene‐styrene ‐ ‐ Graphite 0.385 ‐ ‐ Tetrafluorethylene 0.07 Source: IEK‐STE 2015 IEK‐STE 2015
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