Gasification and Partial Oxidation

In addition to gasification, other oxidative treatments of plastic and rubber wastes, excluding total combustion, are described in this chapter. These methods, although relatively unknown, may be of great interest in the future for the chemical degradation of polymeric wastes. 

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Techniques for the chemical recycling of plastics into monomers and petrochemical feedstocks are described, including chemical and thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification and partial oxidation. BRITISH PETROLEUM CO.PLC... 

The main types of feedstock recycling processes can be summarised as chemical depolymerisation, gasification and partial oxidation, thermal degradation, catalytic cracking and reforming, and hydrogenation [852663]. The current advanced thermal treatments are as follows [a.372]. 

Coal gasification and partial oxidation alternatives appear to be niche applications that fit only in select and special cases. These processes are more complex and less reliable than steam reforming and are higher in capital cost. Nonetheless, future special-purpose applications may favor these technologies, such as in combined cycle power generation. In this case, a coal gas feed linked to a liquid-phase synloop may be an attractive design alternative. 

Gasification coupled with water-gas shift is the most widely practiced process route for biomass to hydrogen. Thermal, steam, and partial oxidation gasification technologies are under development. Feedstocks include both dedicated crops and agricultural and forest product residues of hardwood, softwood, and herbaceous species. 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

The gas feed stream is split, recycle CO2 is added to each stream and the combined streams are fed to each of the two gasification trains. Oxygen from the Air Separation Unit (ASU) is preheated by steam, split and fed to the two gasification trains. Partial oxidation and reforming reactions take place in the Gasifiers. 

The rapid technical progress in the hydrocarbon based technologies of steam reforming and partial oxidation made it possible to generate the synthesis gas at a pressure level sufficient for the C02 removal operation. As gasification proceeds with a considerable volume increase and feedstocks such as natural gas are usually already available under pressure at battery limits, considerable savings in compression energy are achieved in this way. 

With the exception of the Koppers-Totzek coal gasification process, which operates at near atmospheric pressure, all modern gasification processes operate at elevated pressure. Steam reforming of light hydrocarbons at 30-40 bar and partial oxidation of heavy hydrocarbons at 40-90 bar are generally used. 

The FT process is well known and already applied on a large scale [9,10,11,12]. Currently, the two players that operate commercial Fischer-Tropsch plants are Shell and Sasol. In the Sasol and Shell plants gasification of coal and partial oxidation of natural gas, respectively, produce the syngas for the FT synthesis with well-defined compositions. Shell operates the SMDS (Shell Middle Distillate Synthesis) process in Bintulu, Malaysia, which produces heavy waxes with a cobalt catalyst in multi-tubular fixed bed reactors. Sasol in South Afirica uses iron catalysts and operates several types of reactors, of which the slurry bubble column reactor is the most versatile (i.e. applied in the Sasol Slurry Phase Distillate SSPD),... 

Partial oxidation of hydrocarbons can also be used to produce synthesis gas. Partial oxidation, when used for conversion of a solid such as coal or petroleum coke, is generally referred to as gasification. When applied to gaseous or liquid feeds, it is usually called partial oxidation (POX). In principle, however, the two processes are essentially the same. Gasification or partial oxidation takes place at high temperature and pressure in the presence of a small amount of steam and either air or pure oxygen. High... 

The incineration process can be subdivided into the partial processes drying, outgassing, gasification, and complete oxidation G ig. 4) [17]. These idealized processes may overlap both spatially and in time and influence each other. Pyrolytic and gasification methods involve adjustment of the framework conditions so as to favor selected processes. 

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