Fuel 89 (2010) 1763–1783 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Review article Production of synthetic natural gas (SNG) from coal and dry biomass – A technology review from 1950 to 2009 Jan Kopyscinski, Tilman J. Schildhauer *, Serge M.A. Biollaz General Energy Research Department, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland article info abstract Article history: SNG production from coal or biomass is considered again due to rising prices for natural gas, the wish for Received 15 October 2009 less dependency from natural gas imports and the opportunity of reducing green house gases by CO2 cap- Received in revised form 21 January 2010 ture and sequestration. Coal and solid dry biomass (e.g., wood and straw) have to be converted to SNG by Accepted 26 January 2010 thermo-chemical processes (gasification followed by gas cleaning, conditioning, methanation of the pro- Available online 6 February 2010 ducer gas and subsequent gas upgrading). During the 1970s, a number of methanation processes have Herrn Dr. Samuel Stucki zum 65. Geburtstag been developed comprising both fixed bed and fluidised bed methanation. Meanwhile several new pro- cesses are under development, especially with a focus on the conversion of biomass. While coal based Keywords: systems usually involve high pressure cold gas cleaning steps, biomass based systems require, due to Dry biomass Coal the smaller unit size, different gas cleaning strategies. Moreover, the ethylene content of a few percent, Fluidised bed typical for methane-rich producer gas from biomass gasifiers, is a challenge for the long-term catalyst Fixed bed stability in adiabatic fixed bed methanation due to the inherent high temperatures. Methanation This paper reviews the processes developed for the production of SNG from coal during the sixties and seventies and the recent developments for SNG production from coal and from dry biomass. Ó 2010 Elsevier Ltd. All rights reserved. Contents 1. Introduction . ..................................................................................................... 1764 2. Technologies for the production of SNG from solid carbon sources . ............................................ 1764 3. Earlier process development for SNG from coal. ............................................................... 1765 3.1. Fixed bed methanation . ........................................................................................ 1766 3.1.1. Lurgi process. ............................................................................. 1766 3.1.2. TREMP process (within the ADAM and EVA project) . .......................................................... 1768 3.1.3. Conoco/BGC process . ............................................................................. 1769 3.1.4. HICOM process . ............................................................................. 1769 3.1.5. Linde process . ............................................................................. 1770 3.1.6. RMP process . ............................................................................. 1770 3.1.7. ICI/Koppers process . ............................................................................. 1771 3.2. Fluidised bed methanation . ........................................................................ 1772 3.2.1. Bureau of Mines . ............................................................................. 1772 3.2.2. Bi-Gas project . ............................................................................. 1772 3.2.3. Comflux process . ............................................................................. 1774 3.3. Other concepts. ........................................................................................ 1774 3.3.1. Synthane projects . ............................................................................. 1774 3.3.2. Catalytic coal gasification. ............................................................................. 1775 3.3.3. Liquid phase methanation . ............................................................................. 1776 4. Recent developments of SNG from coal and biomass . ............................................................... 1778 4.1. SNG from coal . ........................................................................................ 1778 4.1.1. Great point energy . ............................................................................. 1779 4.1.2. Research Triangle Institute. ............................................................................. 1779 4.1.3. Hydrogasification process . ............................................................................. 1779 * Corresponding author. E-mail address: [email protected] (T.J. Schildhauer). 0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.01.027 1764 J. Kopyscinski et al. / Fuel 89 (2010) 1763–1783 4.2. SNG from biomass.............................................................................................. 1780 4.2.1. Energy Research Center of the Netherlands (ECN) . ............................................. 1780 4.2.2. Center for Solar Energy and Hydrogen Research (ZSW). ............................................. 1780 4.2.3. Paul-Scherrer Institut (PSI)................................................................................ 1781 4.3. Announced commercial international SNG projects . ........................................................... 1781 5. Conclusion . ........................................................................................................ 1782 Acknowledgments . ........................................................................................ 1782 References . ........................................................................................................ 1782 1. Introduction This review focuses on the methanation processes developed for the production of SNG from coal during the sixties and Up to now, the production of fuels and chemicals in most coun- seventies (mostly in US, Germany) and on the recent developments tries is based predominantly on oil and, to a minor extent, natural concerning new processes for SNG production from coal and from gas (NG). It is well known that the reserves of oil and natural gas dry biomass via thermal gasification. are limited to a range of 40–60 years [1]. In contrary, the reserves of coal will last for more than 150 years; and biomass is a renew- able energy source. The longer availability, the wish to improve the 2. Technologies for the production of SNG from solid carbon security of the energy supply and the possibility to reduce the sources green house gas emission by means of carbon capture and seques- tration (CCS), are the main motivation to increase the use of these The production of SNG via a thermo-chemical process requires (domestic) resources. several conversion steps, as depicted in Fig. 1. Besides the generation of electricity and liquid fuels (e.g., The first step is the gasification of the solid carbon source (coal, Fischer–Tropsch-diesel (FT-diesel) [2], Dimethylether (DME) [3]), biomass) with steam and/or oxygen and the production of producer also the conversion of these solid feedstock to synthetic or substi- gas, a gas mixture containing mainly H2, CO, CO2,H2O, CH4, and tute natural gas (SNG) has been investigated, a versatile energy some higher hydrocarbons and impurities such as sulphur and carrier that is inter-changeable with Natural Gas (>95% methane, chlorine species. The composition of the producer gas is influenced high HHV). The advantages of SNG are the high conversion effi- to a large extent by the gasification technology, i.e., by the type of ciency, the already existing gas distribution infrastructure such reactor, the gasification agent, and the operating conditions. as pipelines and the well-established and efficient end use technol- The subsequent fuel synthesis process defines the range of per- ogies, e.g., CNG cars (Compressed Natural Gas), heating, CHP (com- missible gas compositions and the maximum level of impurities at bined heat and power), power stations. Coal and solid biomass the inlet; therefore gas cleaning and gas conditioning are crucial. have to be converted to SNG by thermo-chemical processes via Gas cleaning shall be understood as the unit operations in which gasification and subsequent methanation, reaching an overall the impurities and catalyst poisons (such as sulphur and chlorine) chemical efficiency e.g., from wood to SNG up to 65% (chemical en- are removed from the producer gas. In contrary, gas conditioning ergy output of SNG compared to chemical energy input of wood) summarises all processes in which component of the producer gas are converted in such a way, that the resulting composition [4,5]. It was shown that with increasing CH4 content in the pro- ducer gas, the overall chemical efficiency is increased as this is suitable for the main application (i.e., for the fuel synthesis). way, less heat of reaction has to be removed in the methanation The most common conditioning steps are steam reforming and water gas shift reaction as shown in Eqs. (1) and (2). step [5]. Interestingly, the conversion to CH4 allows for easy and (cost) effective carbon dioxide removal (CCS) as the separation of 0 CxHy þ xH2O $ x CO þðx þ y=2ÞH2 DHR > 0 ð1Þ a highly concentrated CO2-stream is inherent to all SNG-processes. 0 Wet biomass such as crops, sewage sludge and manure can be CO þ H2O $