Gasification Plants for Chemical Production: The Impact of Carbon Utilization on CO2 Capture from the Facility

Abstract

Coal and other disadvantaged fuels such as petroleum coke and refinery bottoms can be used for the production of chemicals around the world. Coal is an established feedstock in gasification and has been the primary focus in markets like China, where the use of coal to chemicals is needed due to limited access to oil and natural gas reserves. Disadvantaged feedstocks such as petroleum coke and heavy residues are currently experiencing a shift in market utilization. New legislation on criteria pollutants in countries like India and IMO2020 legislation are reducing the size of petroleum coke and residue feedstock end markets. The need to dispose of these disadvantaged feedstocks has created new project opportunities for gasification plants. However, with the new opportunities come increasing pressures to lower the CO2 but also increasing the opportunity to take advantage of CO2 emission reduction benefits and/or to deploy the CO2 for enhanced oil recovery. Air Products provides high quality technical solutions as a technology supplier, process integrator and operator. This paper will present our unique perspective on the amenable streams for CO2 capture within the gasification plant, thoughts on how the technologies are developing to further reduce the overall CO2 footprint of a coal to syngas facility, and what the major driving forces are present in selecting technologies and process options. Gasification produces CO2 as a natural byproduct of the reactions taking place in the gasifier to produce syngas as well as downstream water gas shift reactions. The high temperatures and pressures that various gasification and shift processes can operate under provide potential capture points in the plant flowsheet depending on the quantity and purity of CO2 needed. In addition, product syngas requirements dictate the purity and CO to H2 ratio of the product syngas which has a direct influence over the amount of CO2 available to capture from the product syngas streams. Pressurized CO2 sources are a more cost effective way to capture high levels of CO2. As compared to SMR technologies in which approximately 50% of the CO2 is at pressure, solid and liquid gasification technologies contain almost all of the CO2 within the pressurized syngas stream. The amenable product stream locations vary in quantity, purity, and pressure of CO2. Therefore, the degree of capture from the plant is an important variable when selecting the location and technology employed to capture at a specific facility. Gasification also has the advantages of heat recovery from the process to produce steam which can offset the steam demand from low pressure CO2 sources like on purpose boilers. Heat recovery and integration options are core to producing an economic solution to the CO2 capture. Various technologies exist for the removal of CO2 from gasification plants. The methanol based Rectisol process is one technology employed in gasification plants for the effective removal of CO2 from the pressurized gasification syngas streams. It is a proven technology for purifying the syngas stream, but it is not the only technology which can be employed to capture CO2. Numerous studies on decarbonized fuels have outlined Rectisol as well as other acid gas removal technologies for power production. In this paper, the focus will be on revisiting these standby technology options and introducing additional technologies, like Air Products Sour PSA technology, that provide options to capture various levels and purities of CO2, for the solid or liquid feedstock to syngas markets. Currently, Air Products has formed a joint venture with the Luan Coal Group to operate a large-scale gasification plant which converts coal to liquids. The carbon in the coal does not leave the facility as CO2 as in decarbonized power production processes. A significant portion of the carbon is incorporated into the final product from the syngas. This utilization of carbon in the products influences the amenable envelope of technologies that can be used to capture CO2 from the plant. Maximizing the carbon that resides in product molecules provides an interesting twist on previous decarbonized power carbon capture studies. Maximizing carbon utilization provides insight into how to design the balance of plant and what technologies could be developed that would directly impact the material balance as well as the CO2 emissions from the overall facility. Air Products is uniquely positioned to analyze the technical challenges of capturing CO2 from gasification facilities. Identifying cost effective solutions to individual opportunities and the technical driving force influencing design choices will be discussed in this paper.