Deploying plasma arc reforming to a commercial coal to liquid process : a techno-economic study

Abstract

The coal to liquids (CTL) process has played an important role in the supply security of liquid fuels and petrochemicals in South Africa and has the potential of doing the same for coal rich countries globally. Considering the abundance of coal reserves relative to other fossil fuels, coal is probably going to be instrumental as a feedstock for the production of oil for longer than crude oil and gas. However, the CTL process has challenges that include high capital cost, low carbon efficiency and high greenhouse gas emissions. Further, as climate change policies become more widely accepted, the cost implications may threaten the viability and competitiveness of the coal to liquid process. These challenges could be mitigated by the application of cleaner production as a process improvement initiative in commercial coal to liquids. Process redesign to use cleaner and more efficient technology is promising for implementation to coal to liquids. One re-design option would be to integrate plasma arc reforming (PAR), which converts greenhouse gases in by-product streams to syngas. Redesigning a coal to liquid process to use PAR instead of auto thermal reforming has the potential to improve carbon efficiency, reducing emissions and possibly capital requirements in the process. Though it has such potential, PAR remains at laboratory scale, which brings to question whether it would be feasible and viable to deploy plasma arc reforming to a commercial coal to liquid process. This thesis explores the feasibility and viability of deploying plasma arc reforming to a coal to liquid process. First, a technology assessment was done to evaluate the most suitable configuration for deployment to coal to liquids and evaluating its scalability, commercial development status and efficacy in improving carbon efficiency. After that, the process effects of deploying plasma arc reforming were quantified. Finally, the impact of deploying plasma arc reforming on economic performance of coal to liquids was evaluated. Technology screening shows that, a plasma reactor using carbon dioxide as a plasma gas has the best balance between performance and compatibility with coal to liquids. The deployment of plasma arc reforming is capable of improving the carbon efficiency of a coal to liquid process by up to 15%. It was also found that it is feasible to scale up plasma reformers to commercial scale using commercially available components. However, complete reformers are not yet ready for commercial applications and require development. Kinetic characterisation is key to the reduction of technology risk. The improvement in carbon efficiency translates to 15% (by mass) reduction of coal, 32% reduction of oxygen and 20% reduction of steam requirements for process needs. This is accompanied by the reduction of required equipment capacities for gasification, air separation and steam generation equipment. Reduction of required steam generation equipment is accompanied by a substantial reduction in dilute greenhouse gas emissions that would be difficult to manage by sequestration or other means and a reduction of water requirements. However, use of plasma arc reforming requires 49% additional electrical energy and leads to externalised emissions if sourced from fossil powered power plants. Hence, procurement of low carbon electricity would be desirable. These process changes have an impact on the economic performance of coal to liquids, with impacts on the capital and operating requirements. In the absence of carbon tax, the deployment of plasma arc reforming reduced the break-even price from a baseline cost of $80.95/bbl. to $77.42/bbl. When considering carbon tax equivalent to the proposed regime for South Africa, at an equivalent of $4.80/ton, the PAR modified plant requires an oil price of $81.57/bbl. versus $88.39 required by a conventional plant. For all configurations evaluated, the project net present value was greater than zero and the internal rate of return exceeded the hurdle rate, which was based on the Sasol hurdle rate for a coal to liquid project. From the findings, it was concluded that it is feasible to deploy plasma arc reforming to a commercial coal to liquid process. The economic measures evaluated in the study support that a plasma arc reforming modified coal to liquids plant would be viable. However, the carbon-pricing regime in act and the cost of low carbon electricity have a significant influence on the crude price that provides sufficient confidence to support investments into such a venture