Carbon dioxide utilisation for carbamide production by application of the coupled UCG-urea process

Abstract

World-wide coal reserves can supply the global demand for primary energy for several centuries. However, low thickness and structural complexity may constrain the economic exploitation of many coal deposits. Taking into account these circumstances, underground coal gasification (UCG) can offer an economical and sustainable approach for coal exploitation and subsequent feedstock generation from the syngas. The UCG process produces a high-calorific synthesis gas mainly consisting of methane, hydrogen and carbon dioxide, which can be used for electricity generation or feedstock production at the surface. Considering the latter, the Urea process can be applied to establish the nitrogen based fertilizer carbamide (CH4N2O). The required feedstock for carbamide production in the Urea process can be supplied by UCG syngas. The aim of the present study was the development of an integrated carbon utilisation concept based on the coupled UCG-Urea process. A significant amount of carbon dioxide from the UCG synthesis gas is required for carbamide production in the Urea process, while the excessive carbon dioxide can be re-injected into the cavities resulting in the coal seams and surrounding strata after the gasification process. Thus, a new approach for utilisation of carbon dioxide resulting from coal combustion was developed to provide a coupled technology also comprising geological storage of excessive carbon dioxide. A theoretical feasibility study considering UCG-Urea process economics and potentials of UCG and carbon dioxide storage in the gasified strata was conducted for a selected study area in northern Bangladesh revealing the high competitiveness of the combined technology on the international feedstock markets.