Maria Sudiro

Synthetic Natural Gas (SNG) from Coal and Biomass: a Survey of Existing Process Technologies, Open Issues and Perspectives

Natural gas is a well known energy carrier. It is often used for producing heat and power, but can also be applied as a fuel in the transport sector. The production of synthetic natural gas (SNG) from coal or biomass is an interesting opportunity for both exploiting coal and biomass, and for replacing oil products for transportation and other uses. SNG has many important advantages with respect to other synfuels: it can be transported efficiently and cheaply using existing natural gas pipelines and distributing networks, it is an easily convertible feedstock, both in natural-gas combined-cycle power plants and in petrochemical facilities, it can count on a high social acceptance with respect to coal, and it can be stored underground, enabling efficient operation throughout the year independently of a fluctuating demand. Unfortunately, the commercial deployment of technologies for the production of SNG is currently constrained by technical barriers, so that more research is required before extensive applications on the industrial scale can be achieved. An important issue to be addressed is the strong exothermicity of the methane formation reactions, so that conventional fixed-bed catalytic reactors cannot be safely used (Sudiro et al., 2009). Following the 1970s energy crisis much work has been initiated in the US on coal-to-SNG: SNG process technologies and catalysts were developed and tested extensively. But most have been cancelled in the 1980 because of the changing energy picture. One industrial plant has actually been realized in North Dakota, which began operating in July 1984 and today produces more than 54 billion standard cubic feet of synthetic natural gas annually (1.53 billion Nm3/yr). Coal consumption is about 6 million tons each year. The heart of this plant is a building containing 14 gasifiers (www.dakotagas.com). Nowadays, the rise of natural gas prices have created a strong interest in producing SNG from the cheaper and much more abundant coal. A renewed interest in basing more energy consumption on coal and petcoke has resulted in a revival of several older technologies that have been enhanced to improve efficiency and to lower investment cost. Methanation is used as the final syngas purification step in the production of ammonia, but methanation for SNG production is more complex. The main industrial application of methanation has been the removal of CO from H2-rich feed gases in ammonia plants. With 5

Simulation of a structured catalytic reactor for exothermic methanation reactions producing synthetic natural gas

Abstract Aim of this work is a theoretical investigation of the catalytic methanation reactions in externally cooled tubular reactors filled with novel monolithic catalysts with high thermal conductivity. Using the general purpose modelling tool gProms™ we have developed a steady-state, heterogeneous ID model, representing a single, externally cooled reactor tube loaded with cylindrical honeycomb catalysts with square channels, made of conductive material. The model equations include mass and energy balances for the gas and solid phases and the momentum balance for the gas phase. Two reactions are considered: carbon monoxide and carbon dioxide methanation, whose rate equations are taken from the literature. By reactor simulation it is shown that the problem of temperature control typical of fixed-bed methanation reactors can be overcome by the monolith reactor herein proposed. The effects of space velocity on conversion and temperature profiles are discussed, with a fixed geometrical configuration of the monolithic reactor.

Production of Synthetic Gasoline and Diesel Fuels by Alternative Processes Using Natural Gas, Coal and Biomass: Process Simulation and Economic Analysis

The problem of producing synthetic liquid fuels by alternative routes is addressed. Industrial processes known as Gas To Liquid (GTL), Coal To Liquid (CTL) and Biomass To Liquid (BTL) are considered: they use natural gas, coal and biomass as feedstocks, respectively. By means of process simulation, it is shown that the fuel produced on a weight basis per unit of feedstock (natural gas, coal and wood) are 66.7, 32.5 and 16.8%, respectively; in addition, the CO2 emitted per unit mass of liquid fuel is 0.90 kg CO2/kg for GTL, 4.79 kg CO2/kg for CTL and 6.08 kg CO2/kg for BTL process. In this last case, carbon dioxide is not an issue because it derives from a renewable source. The evaluation of production costs of synthetic fuel for a GTL process is carried out under two different scenaries: a plant localised where natural gas is readily available, and another one built far from the country where the gas is produced. A comparison between the costs of synthetic fuels from a GTL process and conventional fuel from oil refining is carried out to show the competitiveness of this alternative fuel. A financial analysis permits to conclude that, if a GTL plant is localised where the natural gas is extracted, the return of investment is after 2.4 years, whereas it changes to 6.9 years if the plant is located in western industrialised countries.