Reengineered Feedstocks for Coal Combustion Emissions Control

Coal combustion is an important process for electricity production in the United States. However, coal power plants produce gases such as SO_x, NO_x and HCl, which can lead to environmental problems including formation of acid rain.  Increasingly strict regulations, such as the Clean Air Act, mandate the reduction of emissions from coal combustion facilities. Currently, the U.S. produces ~7 quadrillion BTUs of electrical power per year from coal, constituting 42% of all electrical energy being produced in the country (in 2011).[1]  A number of processes exist for cleaning these emissions to lower levels (e.g. wet scrubbing the exhaust gas), but the augmentation of new chemical processing equipment to existing power plant systems will introduce significant costs, greater water consumption, and decreased energy efficiency.  A transformational idea is to develop an energy-rich coal co-reactant from post-recycled materials which can be utilized in existing coal combustion facilities as both a fuel substitute and a sorbent of harmful process emissions.

A new coal-reaction technology called ReEngineered Feedstock^TM (ReEF) has been developed by ReCommunity Inc.[2, 3]  ReEF is designed to be physically and chemically compatible to the coal that the coal fired boiler utilizes, and can be directly co-reacted with coal with fuel feeding and handling infrastructure in existing coal combustion systems. In energy basis, it can replace up to 30% of coal with post recycling materials, which otherwise would be landfilled, in existing pulverized coal combustion facilities. The ReEF combines post recycling fiber products and plastics from local residential and commercial municipal solid waste that are impregnated with sorbents or chemical additives forming a Re-engineered fuel which can serve to trap emissions such as SO_x.  The ReEF co-reactant and emission reduction technology will be demonstrated on a laboratory scale using a fluidized bed combustor (FBC) system[4-7].  Although the addition of sorbents such as limestone, bauxite, kaolinite and CaO to furnaces, to control the emission of toxic trace elements from coal combustion, have been previously reported in laboratory, pilot or commercial scale fluid bed combustors [5], the effectiveness of these technologies has been proven limited and thus had little commercial success. This study will be undertaken to demonstrate the effectiveness of the ReEF as an innovative and efficient reactant co-feed for coal combustion and emission reduction.  Optimization of combustor temperature, feed rate, fluidization velocity and air to feed ratio will be determined for this system.  This technology has the potential to significantly impact the economics and environmental impact of both waste management and coal fired power plants.

References

1.             Refer to website http://www.eia.gov 2012.

2.             Bohlig, J.; Bai, D. Engineered Fuel Feed Stock. U. S. Patent No. 8,157,874.

3.             Bohlig, J.; Bai, D. Engineered Fuel Feed Stock. U. S. Patent No. 8,157,875.

4.             Stenger Jr., H. G.; Meyer, E. C., Laboratory-Scale Coal Combustor for Flue Gas Emission Studies. Energy & Fuels 1992, 6, 277-286.

5.             Cheng, J. F.; H. C. Zeng; Z. H. Zhang; Xu, M. H., The effects of solid absorbents on the emission of trace elements, SO₂ and NO_x during coal combustion. Int. J. Energy Res. 2001, 25, 1043-1052.

6.             Cao, Y.; Hongchang Zhou; Junjie Fan; Houying Zhao; Tuo Zhou; Pauline Hack; Chia-Chun Chan; Jian-Chang Liou; Pan, W., Mercury Emissions during Cofiring of Sub-bituminous Coal and Biomass (Chicken Waste, Wood, Coffee Residue, and Tobacco Stalk) in a Laboratory-Scale Fluidized Bed Combustor. Environ. Sci. Technol. 2008, 42, 9378–9384.

7.             Li, S.; Shuang Deng; Andy Wu; Pan, W.-P., Impact of the Addition of Chicken Litter on Mercury Speciation and Emissions from Coal Combustion in a Laboratory-Scale Fluidized Bed Combustor. Energy & Fuels 2008, 22, 2236–2240.