Assessment of Fischer Tropsch Hybrid CTL and BTL

Researchers from the US and China collaborated to assess the "well to wheels" model of production of diesel from combined coal and biomass gasification, using F-T synthesis plus power generation from syngas combustion. Abstract:

This study expands and uses the GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model to assess the effects of carbon capture and storage (CCS) technology and cellulosic biomass and coal cofeeding in Fischer−Tropsch (FT) plants on energy use and greenhouse gas (GHG) emissions of FT diesel (FTD). To demonstrate the influence of the coproduct credit methods on FTD life-cycle analysis (LCA) results, two allocation methods based on the energy value and the market revenue of different products and a hybrid method are employed. With the energy-based allocation method, fossil energy use of FTD is less than that of petroleum diesel, and GHG emissions of FTD could be close to zero or even less than zero with CCS when forest residue accounts for 55% or more of the total dry mass input to FTD plants. Without CCS, GHG emissions are reduced to a level equivalent to that from petroleum diesel plants when forest residue accounts for 61% of the total dry mass input. Moreover, we show that coproduct method selection is crucial for LCA results of FTD when a large amount of coproducts is produced. _ACS_via_GCC

Technologies for carbon capture are still at a primitive and expensive stage -- which means that CCS should be omitted from early plant design and implementation. As it becomes economical to capture and use CO2 as a valuable co-product of the overall process, it will make more sense to implement CCS. Otherwise, the terrestrial and oceanic biosphere can make excellent use of whatever CO2 humans are capable of providing it.

...with the energy-based allocation method, fossil energy use of FTD is less than that of petroleum diesel, and GHG emissions of FTD could be close to zero or even less than zero with CCS when forest residue accounts for 55% or more of the total dry mass input to FTD plants. Without CCS, GHG emissions are reduced to a level equivalent to that from petroleum diesel plants when forest residue accounts for 61% of the total dry mass input. They also found that coproduct method selection is crucial for LCA results of FTD when a large amount of coproducts is produced.

The system boundary for the study is from wells to wheels (WTW), including a well-to-pump (WTP) stage covering the production and transportation of feedstock and the production, transportation, and distribution of fuel and a pump-to-wheel (PTW) stage covering vehicle operational activities.

In the FT process, solid feedstocks such as coal and biomass, are gasified to produce syngas, which is cleaned of CO2 and sulfur compounds and then send to FT reactors where a catalyst is used to convert CO and hydrogen into the desired hydrocarbon products. The CO2 may be vented or captured and sequestered (with the CCS technology). During FTD production, electricity could be produced from unconverted syngas, some of which could be exported to the electric grid as a coproduct. In addition to synthetic diesel FTD and electricity, FTD plants produce a mixture of hydrocarbons, the liquid portion of which is refined into finished FT diesel, naphtha (or gasoline).

There are two general designs for FTD production: recycling (RC) design and once-through (OT) design. In the RC design, unconverted syngas is recycled back for additional conversion, and the final tail gas is used for power generation. The OT design passes the syngas only once through a synthesis reactor and maximizes the power generation from the plant. _GCC

Simple gasification and power generation from syngas, via gas turbine, is the most direct and clean use for coal or biomass energy. Producing liquid fuels from syngas requires energy, thus reducing the overall efficiency. But given the huge infrastructure for use of liquid fuels, it makes economic sense to convert coal, gas, and biomass to liquid fuels -- as long as our goals are not twisted beyond recognition by the carbon hysterics and dieoff.orgiasts.