Coke oven gas, purification

Figure 17 Ammonia hydrogen sulfide circulation scrubbing process for the coke oven gas purification (right) and H2S absorber (left).

Removal of harmful substances Coke oven gas purification Carbon dioxide removal by amines/ amine blends/ hot potassium carbonate solutions NOx removal Gas purification 63, 89, 91, 105-107... 

Ammonia, hydrogen sulfide, and carbon dioxide are major impurities in coke oven gas (COG). In addition to these three components, COG often contains caibon disulfide, carbonyl sulfide, hydrogen cyanide, organic acids, pyridine, phenol, and other impurities, which can cause problems with conventional amine plants. The presence of large quantities of ammonia in these gases naturally led to consideration of its use for removal of HjS and CO2, and several ammonia-based coke oven gas purification processes have been developed and commercialized. 

Processes that use aqueous ammonia to remove H2S and CO2 are still offered for coke-oven gas purification, and many such plants are in operation in the U.S. and Europe however, it appears that the trend for new operations is toward the use of other absorbents. Other absorption processes that may be applicable for COG purification include the Takahax, Stretford, Vacuum Carbonate, Potassium Carbonate, and Sulfiban (MEA) processes. These processes can be designed to avoid serious adverse effects of trace impurities in the gas, and generally provide somewhat higher H2S removal efficiency than ammonia scrubbing. The processes are described in detail in other chapters (see index). 

In Japan, there is a project aimed at capturing the considerable volume of hydrogen gas which can be obtained as a by-product steel production. R D will focus on the purification process of fuel from coke oven gas to an acceptable level for fuel cell utilisation. METI, the Japan Research and Development Centre for Metals and Nippon Steel are working on the project with a 2003 budget allocation of 549 million. Japan also operates the 4C/.f project which aimsto develop an optimum coal gasifier for fuel cells and the establishment of gas clean-up system for purification of coal gas to the acceptable level for utilisation for MCFC and SOFC. The budget allocations for 2000-2003 total 4.6 billion. 

COAL TAR AND DERIVATIVES. CAS 65996-93-2. Coal tar constitutes the major part of the liquid condensate obtained from the dry" distillation or carbonization of coal (mostly bituminous) to coke. The three inajor products of this distillation are (I) metallurgical coke. (2) gas which is suitable as a fuel after appropriate chemical treatment, and (3> condensable liquids which leave the coke oven along with the gas and which are constituted principally of ammonia liquor and coal tar. The condensable materials and gas impurities are separated from gas in the condensation and purification train of the coke oven plant. The purified coke oven gas is used as fuel in heal the coke ovens and steel producing furnaces. Prior to the widespread use of natural gas as a dnmeslic fuel, coke oven gas was widely used for this purpose after additional purification as residential fuel. 

Benzols are essentially produced by the purification of crude gas, with a small part produced by tar distillation. Coke oven gas has the following average composition ... 

In early days of Phase I, the predominant feedstock for ammonia synthesis was coke. Synthesis gas was either produced at atmospheric pressure in water-gas shift units or prepared by purification of coke oven gas. In these early plants, the process effluents from the ammonia converter were cooled without recovery of heat. Due to the lack of technology regarding the attainable size of the converter pressure shell, the physical dimensions of the converter were limiting factors for the achievable production capacity. Therefore, a particular emphasis was placed on maximization of the production capacity for a given volume [139]. During World War II, several plants were built in the United States, based on natural gas feedstock. Since then, natural... 

Coke-Oven Gas - Before the 1940s, coke-oven gas was used for a large portion of ammonia production. Coke-oven gas contains about 55% Hg, 25% CH4, 8% CO, 6% N2, minor amounts of higher hydrocarbons, CO2, and various impurities. Presumably, it could be used for ammonia production by steam reforming after purification, but the usual practice is to separate the hydro-... 

Figure 3.13 Flow diagram for the purification of coke oven gas...

Since most of the early gas purification work was related to the processing of manufactured and coke-oven gas streams, which contain ammonia as well as hydrogen sulfide, attempts were made to develop combination processes that would remove both impurities while producing marketable products such as ammonium sulfate and elemental sulfur. The first processes of this type were based on a recirculating solution of ammonium polythionate. They proved technically feasible, but quite complex, and were not commercially successful. 

Field test data showing the effects of natural gas composition and flow rate are given by Enneking (1966). The use of adsorption to recover hydrocarbons from gas streams at refineries and petrochemical plants is described by Cantrell (1982). The recovery of benzol (a benzene-rich light oil) from manufactured and coke-oven gas streams was formerly an important application of activated carbon adsorption, but is no longer considered significant. A typical benzol removal installation is described by Howell (1943) and Walker et al. (1944). Hydrocarbon recovery processes are not described in detail herein because of their similarity to solvent recovery processes and the fact that they are intended primarily for recovery, not gas purification. 

The removal of hydrocarbon vapors from gas streams by absorption in liquid oils is an important part of many industrial operations. In some cases, such as natural gasoline recovery, the absorption step is but a portion of a refining process that produces several commercial products, and the gas purification aspects of the operation are of little importance. In other cases, such as the removal of aromatics from coke-oven gas, the absorption process serves to improve the value of the product gas. Processes for the removal of light oil (primarily benzene) and naphthalene from coke-oven gas are described in this section. 

Hydrogen sulfide in manufactured gases may range from approximately 2.30 g/m (100 gr/100 ft ) in blue and carbureted water gas to sever hundred grains in coal- and coke-oven gases. Another important sulfur impurity is carbon disulfide, which may be present in amounts varying from 0.007 to 0.07 percent by volume. Smaller amounts of carbon oj sulfide, mercaptans, and thiophene may be found. However, most of the impurities are removed during the purification process and either do not exist in the finished product or are present in only trace amounts. 

There are two main processes in the thioarsenate category. The first, the Thylox process, was developed in the late twenties and used in the U.S. for many years, especially for the purification of coke-oven and other manufactured gases. The second, the Giammarco-Vetro-coke (G-V) process, is a dual H2S/CO2 gas sweetening process introduced in Italy in 1955, which was extensively used in Europe and Asia, especially in applications where the H2S concentration in the feed gas was relatively low. 

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