Development and Application of a LCA Model for Coal Conversion Products (Coal to Y)

Transcription

1 Development and Application of a LCA Model for Coal Conversion Products (Coal to Y) Christian Nissing, Loïc Coënt and Nathalie Girault Abstract TOTAL Gas & Power launched a series of development studies in order to investigate the potential for coal conversion projects (coal to Y) for the production of fuels and primary products for the petrochemical industry. A crucial role is played by the aspects of carbon capture and storage (CCS). Based on these studies, a methodology and a model for life cycle analysis (LCA) were developed in order to understand the environmental impacts associated with Coal to Y conversion routes, especially regarding GHG emissions, water consumption, and energy efficiency. The model was designed around the need for adaptability to a) the geographic location of the coal mine and the coal to Y conversion plant, and b) the final products (e.g. methanol, DME, SNG and FT diesel) and their respective markets. By applying the model to a potential coal to methanol application by utilising original data and in-house expert advice, first results were generated, giving valuable insights especially into the critical elements of the CO 2 management system. The developed LCA model is a powerful tool that can assist in analysing clean coal studies. 1 Introduction 1.1 Background and aim Against the background of a growing global energy demand, TOTAL is thriving to diversify its product portfolio as well as its production means in order to meet this demand in a sustainable manner. Within this context, detailed engineering studies have been carried out by the chemical processes department of TOTAL Gas & Power on 5 different coal conversion routes (coal to Y) for fuels and primary materials for the petrochemical industry, including carbon capture and sequestration (CCS) options. C. Nissing ( ) N. Girault TOTAL Gas & Power, Paris, France christian.nissing@total.com L. Coënt TOTAL Gas & Power, Paris, France KTH Royal Institute of Technology, Stockholm, Sweden M. Finkbeiner (ed.), Towards Life Cycle Sustainability Management, 469 DOI / _46, Springer Science+Business Media B.V. 2011

2 470 Christian Nissing et al. Based on these studies, it is the aim of this paper to develop a life cycle assessment (LCA) of the concerned products, focused on the aspects of energy consumption, greenhouse gas emissions (GHG) and water consumption. A special emphasis will be on the development of a LCA model that is adaptable in terms of geographic location of final coal conversion product. The results of the LCAs will help TOTAL to understand the environmental impacts associated with these production routes. 1.2 Approach In order to achieve the aim of this paper, a number of subsequent elements will be developed. Firstly, a literature review of the main areas of interest will be presented. Secondly, a comparative LCA will be developed, including a description of the applied methodology, the scope and goal definition, as well as the generation of results and its interpretation based on a previously established data inventory. The methanol case will be detailed and put into geographic perspective. Finally, a number of conclusions will be formulated and an outlook for future work will be given. 2 Literature review 2.1 Life cycle assessment (LCA) theory The LCA method is defined as the assessment of the environmental impact of a given product or service throughout its entire lifespan. This method is formalised through ISO norm [1]. It includes four compulsory steps, consisting of the goal and scope definition, the life cycle inventory (LCI), the impact evaluation, and its interpretation. These steps can be complemented by two optional steps, which are the sensitivity analysis and the critical review. A number of software tools have been developed in order to assist in the performance of an LCA. The Simapro software package has been utilised to perform the LCA presented in this paper.

3 LCM in the Energy Sector LCA and its interest for TOTAL The interest of the LCA methodology for TOTAL is manifold: Firstly, it can generate inputs for internal information and analysis. Secondly, it can provide a scientific and objective basis for external communication purposes. Thirdly, it is an integral part of the TOTAL EcoSolution label, consisting in a set of stringent criteria a product or service has to meet in order to be considered as having a positive environmental performance [2]. Fourthly, it is of special interest to TOTAL's petrochemical branch, were an emphasis is laid upon the end-of-life management of plastic products [3]. Lastly, for TOTAL's Refining & Marketing branch, it is a compulsory approach for the calculation of GHG reduction rates of biofuels [4]. 2.3 Coal and the environment Coal mining has been performed worldwide throughout history and continues to be an important economic activity. Today, coal is the largest primary source of energy used for the generation of electricity worldwide[5]. The use of coal is coupled to major environmental impacts, which are i.a. the release of carbon dioxide, a GHG which causes climate change and global warming [6], and the impact of water use on flows of rivers and consequential impact on other land-uses[7]. In order to reduce these environmental impacts, there is a trend among coal dependent industry to operate according to the highest environmental standards, which can be formalised through ISO certification [8]. Technical options for the mitigation of GHG emissions include energy efficiency measures and CCS (see section 2.5). 2.4 Coal conversion routes (CTY) Next to coal combustion for electricity generation, coal can be converted via gasification, resulting in a hydrogen rich synthesis gas (syngas). The obtained syngas can in turn be converted to a series of products, ranging from fuels to input

4 472 Christian Nissing et al. feeds for the petrochemical industry. This type of coal conversion is commonly referred to as Coal to Y or CTY conversion. [10] A CTY conversion plant is generally made up of three distinct sections, namely the coal gasification section, the syngas conditioning section, and the product synthesis section. Acid gas removal units (AGRs) are located in the syngas conditioning section, used i.a. for capturing the CO 2 stream. TOTAL investigated the potential of CTY applications. Main results will be presented in section Carbon capture and storage (CCS) CCS is a GHG emissions reduction option which consists in capturing CO 2 at its emission source and its transportation to and injection into a suitable geological structure [9]. It includes three distinct steps: CO 2 capture: There are three generic capture processes for coal power plants, namely post-combustion, pre-combustion and oxy-fuel combustion capture. Similar applications exist for production plants such as cement kilns, alloy smelters, or CTY plants. Compression and transportation: Once separated, the CO 2 is compressed, and transported to a suitable geological storage site, either by truck, train, barge or pipeline. Storage: CO 2 is injected into a suitable geological storage structure, such as saline aquifers, depleted oil & gas fields, or used for enhanced oil recovery (EOR). A good overview on LCAs performed on CCS applications is given by the IEAGHG [10]. 3 Comparative LCA on coal conversion products 3.1 Scope definition Based on the aim of this paper as given in section 1.1, the purpose of this section is to give the scope of the LCA, as well as related information such as its limitations, the functional unit, allocation rules chosen, and the applied impact evaluation methods.

5 LCM in the Energy Sector Underlying TOTAL internal study TOTAL investigated the potential for 5 coal conversion projects (coal to Y) for the production of fuels and primary products for the petrochemical industry [10]. Tab. 1: CTY products, LHVs and main applications (sources: [11], [12]) CTY products LHV [MJ/kg] MET Methanol 19.9 DDME IDME Dimethyl ether, direct and indirect route 28.4 FTD Fischer-Tropsch diesel 44.0 SNG Synthetic Natural Gas 50.0 Examples of application Petrochemical base for MTO process Motor fuel Motor fuel (LPG blending required) Petrochemical base for DTO process Motor fuel (Standard diesel blending required) Stationary heating applications Power generation As given in Tab. 1, each product has a number of different final applications, possibly requiring additional downstream conversion and conditioning steps. For each coal conversion route, a plant design was developed, considering a grass root complex able to operate in a standalone mode with only coal, raw water and start-up power available at plant boundaries. Next to the main product train, i.a. utilities and power block are included to the battery limits. The plant was set to a generic location in North America. [10] Each conversion route has the same input feed, namely 4 Mt/a of coal. Coal requirements for utilities and power block have to be added to this amount. The primary aim of the development study was to perform a comparison of product output, utility requirements, and technical costs. The LCA presented in this paper is based on this study Limitations The products on which the LCA will be performed are the products at the gate of the coal conversion plant. As can be seen in the example given for the MeOH product in Fig. 1, the considered system begins with the coal mining process, followed by its transportation to the coal conversion plant. The conversion unit is split into three parts, namely the coal gasification part, the MeOH synthesis part, and the CCS part. Power is supplied to the gasification unit by a power block (integrated gas combined cycle - IGCC), on which carbon capture is applied as well.

6 474 Christian Nissing et al. Coal, in ground Coal mining Coal Coal Coal Coal MeOH transportation Gasification, to MeOH plant MeOH synthesis, CCS Coal Power generation (IGCC), CCS Elec Surplus elec sold to grid Fig. 1: System limits of Coal-to-MeOH route It has been chosen to perform a 2 nd degree LCA, excluding the infrastructure construction steps, such as mine development or conversion plant construction. The life-cycle impact of infrastructure construction has been considered as minimal, as it is depreciated over the plant lifetime (25 years) Functional unit The functional unit is defined as the quantified performance of a product system used as a reference unit in a LCA [13]. As the considered final products can all be utilised energetically (fuels), the functional unit is set to be "to produce 1 MJ of energy content in the final product" Allocation rule Inputs and outputs of a process which results in different products must be allocated between these products according to explicit rules (allocation rules). [13] An allocation problem appears for the FT route. A co-product of the FT diesel production is naphtha. As only the diesel product is considered in this paper, emissions and consumptions related to the naphtha product are subtracted according to its energy content (application of energy allocation rule) Impact evaluation methods For this paper, the first impact category considered is global warming (midpoint indicator - Simapro IPCC method) [6]. It is quantified by the corresponding amount of GHG emissions, expressed by the indicator "mass of CO 2 equivalent" (gco 2 e). Next to carbon dioxide, other GHG such as methane and nitrous oxide are considered by this indicator. Two others impacts are evaluated: fresh water and primary energy consumption.

7 LCM in the Energy Sector 475 Fresh water consumption takes into consideration water needs along the life-cycle chain. It is expressed in "mass of fresh water used". Fresh water consumption is of specific interest, as it can lead to depletion of water resources and change in flows of rivers (see section 2.3). Primary energy consumption sums up all fossil and nonfossil energy consumptions over the life-cycle chain. The indicator used is "primary energy equivalent used" (MJ-e) [14]. 3.2 Life cycle inventory (LCI) Based on the previously defined scope, the data collected for the different lifecycle steps will be presented in the following sections Mining In order to extract coal from the ground, a mining step is required. For this LCA, an average North-American underground mine has been considered [15]. Electricity, heat, and diesel requirements for mining operation are included. A specific coal type has been considered for the internal study [10] Transportation As the coal mine and the production plant are not located on the same site, transportation of the coal to the conversion plant is required. It is assumed that the distance between mine and process plant is 100 km. The transport system used is freight train transportation, assuming average diesel and electricity consumption [15] Conversion process, utilities and power block All GHG emissions and fresh water requirements were taken into account. All energy requirements for the conversion process and utilities are assumed to be covered by the power block [10]. Due to the relatively low number of start-ups (around once every 3 years), only emissions occurring during the regular operation phase were considered. For the injection of electricity into the local power grid (see section 3.1.4), an average North-American electricity mix has been considered [15].

8 476 Christian Nissing et al Carbon capture and storage (CCS) Carbon capture is realised through AGR units downstream of the gasification trains. Overall CO 2 capture rates range from 84% for FT diesel to 99% for SNG. Energy needs for carbon capture and compression are included in the conversion process, utilities and power block. The CO 2 injection site is located approx. 150 km from the conversion plant. It has been assumed that no further energy requirements for transportation and injection were required. [10] 3.3 Impact evaluation As can be seen in Figure 2, FT diesel generates the highest amount of GHG emissions, amounting to approx. 180g CO 2 e/mj, excl. CCS and grid injection, and a net of approx. 40 gco 2 e/mj. Net GHG emissions for FT diesel are thus twice as high as for DDME, the second highest value. SNG has the lowest net level of GHG emissions. 200,00 150,00 [gco2eq/mj] 100,00 50,00 0,00 50,00 100,00 Total net emissions Grid electricity substitution CO2 to storage Main transformation process Surplus power production Power production for process Resource transportation Resource extraction 150,00 200,00 FTD SNG MET IDME DDME Fig. 2: GHG emissions for 5 CTY products Surplus electricity is accounted for on the emissions side, but also on the credits side via the substitution of grid electricity.

9 LCM in the Energy Sector 477 Furthermore, emissions related to resource extraction are directly dependent on coal needs for the conversion process and IGCC. The efficiency of the conversion process and related power needs is the aspect displaying the highest variability between routes. Finally, the emissions related to transportation are negligible. As shown in Tab. 2, FT diesel production has the highest consumption of primary energy, 1.78 MJ-e/MJ, but also the lowest consumption of fresh water, 0.34 kg/mj. The four other routes have similar fresh water requirements. Fresh water consumption is almost entirely related to the process. The product with the lowest energy requirements is SNG, with 1.16 MJ-e/MJ. Tab. 2: Fresh water and primary energy consumption for 5 CTY products FTD SNG MET IDME DDME Water [kg/mj] Energy [MJ-e/MJ] By comparing Figure 2 and Tab. 2, there seems to be a correlation between energy consumption and GHG emissions. This point needs to be substantiated statistically. 3.4 Interpretation of results Be performing a high level analysis for the most environmentally sound product, a preliminary ranking system has been designed (see Tab. 3). For each impact category, values have been normalised by dividing it by the highest value for each category (the highest normalised value being 1). By adding up the obtained values for each product, combined impact values are obtained. At this stage, no weighting factors have been included. Tab. 3: Preliminary ranking system FTD SNG MET IDME DDME GHG emissions Fresh water consumption Primary energy consumption Sum

10 478 Christian Nissing et al. Results show that the most environmentally friendly product is SNG, whereas the least environmentally sound product is FT diesel according to this approach.in a future step, a more detailed analysis can be developed, including weighting factors according to the attributed importance of each impact category. 3.5 Revisiting the methanol case Methanol is an interesting case, as it is suited for a number of downstream processes such as methanol-to-olefins (MTO) conversion. Its case is thus reviewed in terms of its environmental performance (only GHG emissions) in different world regions, as well as benchmarked against other fossil routes. As can be seen in Fig. 3, three coal-to-methanol scenarios are developed based on TOTAL internal data, respectively located in Asia, North-America and Europe. Furthermore, three scenarios are developed based on CONCAWE data [12], respectively representing a coal-to-methanol, an oil-to-gasoline and an oil-todiesel product. All three products are produced for the European market. For the gasoline and diesel scenarios, the LCA system has been limited to the product at the refinery gate. No final combustion takes place. 300,0 250,0 Total net emissions 200,0 150,0 Grid electricity substitution CO2 storage [g CO2eq/MJ ] 100,0 50,0 0,0 50,0 100,0 150,0 ASIA MET N A MET EU MET EU MET EU GASO EU DIESEL Main transformation process Power import for process Surplus power production Power production for process Regional coal mix Resource transportation Resource extraction 200,0 TOTAL Fig. 3: Methanol from coal vs. conventional fuels CONCAWE As can be seen in Fig. 3, the main difference in the first two scenarios lies in emissions related to mining activities, accounting for approx. 90gCO 2 e/mj for the

11 LCM in the Energy Sector 479 Asian case, and only about 15g CO 2 e/mj for the North-American case. This is mainly due to the difference in meeting energy demands: in Asia, needs are met via low-efficiency pulverised coal boilers, whereas in North-America, needs are met via diesel engines and imports from the electricity grid. The second and third scenarios show that total GHG emissions are comparable for the coal-to-methanol life-cycle in North-America and Europe, although power needs for CO 2 compression have been subtracted for the European case (as no CCS). The third and fourth scenarios were developed in order calibrate the TOTAL model with the CONCAWE study. Finally, the methanol scenarios are compared with the diesel and gasoline scenarios. It can be stated that in order to remain competitive with conventional fuels from oil on a GHG emission basis, the methanol must be produced in either North-America or Europe, and CCS is a necessary prerequisite. If such a plant was to be realised in Asia, North-American or European mining procedures and standards would have to be applied. 4 Conclusion and outlook The aim of this paper was to understand the environmental impacts associated with coal conversion products (CTY), namely GHG emissions, as well as fresh water and energy consumption. LCA has the potential as a method to produce results in order to achieve this aim. It was highlighted that there is a trend in coal dependent industry towards the integration of environmentally sound technology, such as energy efficiency measures and CCS. A comparative LCA based on ISO was presented. The impact evaluation showed that FT diesel has the highest GHG emissions, while having the lowest fresh water consumption. By applying a normalisation approach incl. the three targeted impact categories, SNG showed the best environmental performance. The methanol case was revisited by relocating its life-cycle to different world regions. Results showed that, in order to remain competitive with gasoline or diesel from oil, CCS technology is a prerequisite. Furthermore, European or North-American mining standards need to be applied. In order to refine the obtained results, further material streams need to be looked at, i. a. sulphur and heavy metal emissions. The integration of weighting factors according to the importance of the different environmental impacts will lead to a more informed ranking system for CTY products.

12 480 Christian Nissing et al. References [1] International Organisation for Standardisation (2006) Environmental management-life cycle assessment-principles and framework. ISO,Geneva [2] TOTAL (2009)TOTAL Eco-solutions Guidelines Version 1 [3] TOTAL (2010) Petrochemicals, Plastics end of life management.topics, No. 14 [4] European Parliament and Council, Directive 2009/29/EC on the promotion of the use of energy from renewable sources.official Journal of the European Union Vol. 52 (2009) [5] International Energy Agency Greenhouse Gas R&D Program, < (accessed ) [6] Le Treut H, Somerville R, Cubasch U, Ding Y, Mauritzen C, Mokssit A, Peterson T, Prather M (2007)Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.Cambridge University Press, Cambridge [7] MangenaSJ, BrentAC (2006) Application of a Life Cycle Impact Assessment framework to evaluate and compare environmental performances with economic values of supplied coal products.j Clean Prod 14: [8] International Organisation for Standardisation (2004)ISO Environmental management. ISO, Geneva [9] < (accessed ) [10] IEAGHG (2010)Environmental evaluation of CCS using life cycle assessment (LCA). IEA [11] TOTAL (2009)Coal-to-Y. Final report [12] Edwards R, LarivéJ, Mahieu V,RouveirollesP (2007)Well-to-Wheels analysis of future automotive fuels and power trains in the European context -Well-To-Tank Report Version 2c [13] International Organisation for Standardisation (2006)ISO 14044: Environmental management-life cycle assessment-requirements and guidelines.iso, Geneva [14] FrischknechtR, Jungbluth N et al (2000) Implementation of Life Cycle Impact Assessment Methods.Final report ecoinvent [15] Ecoinvent Centre (2007) Eco-invent data v2.0.final report eco-invent No 1-25