Town gas production

The burners used in domestic appliances at that time were not suitable for use with natural gas, because of its high calorific value. For this reason, natural gas was not used directly until the 1960s. Small cycUc reforming processes were introduced to meet peak demand when the supply of coal gas was insufficient to meet the requirements. Larger plants were installed to meet the needs of larger areas, and the relatively low calorific value of the reformer gas was increased to the required level by the addition of low-molecular-weight hydrocarbons.  

A wide range of catalysts produced by impregnating a-alumina or magnesia with low concentrations of nickel oxide were used in cyclic reformers. These catalysts had to be extremely heat resistant because the process generated carbon which was removed at intervals by burning in air. 

At about the same time the British (ilas Council developed its adiabatic process in which naphtha or fighter hydrocarbons were converted into a high methane content gas with a calorific value of almost 700 Btu per cubic foot. This gas could then be converted into town gas with a calorific value of 500 Btu per cubic foot by continuous steam reforming in a lean gas plant and appropriate blending. Since then the CRG process has also been widely used throu out the world to produce methane rich gas fiom naphtha and LPG. 

The CRG process operates adiabatically in a small single bed reactor. The catalyst has high nickel oxide content and is precipitated under carefully controlled conditions with alumina to give a high activity and thermally stable strac-ture. The finished catalyst is alkalized to prevent carbon formation and is reduced before operation. Steam to carbon ratio can be as low as 1.5 when reforming naphtha to produce town gas. 

When operating with naphtha as feed, the endothermic reforming reaction is dominant at the top of the bed. As the concentrations of both hydrogen and carbon monoxide increase, the exothermic methanation reaction becomes the dominant reaction so that the overall reaction is exothermic. Gradual catalyst deactivation leads to the temperature profile moving down the bed and catalyst fife can be as long as two years. With natural gas feed any hydrocarbons heavier than methane are reformed, the methane steam equilibrium is established, and the overall reaction is endothermic. Operating details are shown in Table 9.16. 

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The above reactions proceed also in the so-called rich-gas processes of British Gas and Lurgi/BASF, which convert naphtha with steam in autothermal reactions in a vessel filled with a special nickel-containing catalyst. It was formerly successfully used for town gas production from naphtha. This reaction may also used as pre-reformer ahead of a conventional tubular steam reforming furnace to convert higher hydrocarbons at low temperature and low S/C ratio into a methane reach gas which can than be reformed in the primary reformer with a standard methane reforming catalyst instead of an alkalized catalyst (Section 4.1.1.3.1). 

This gasification technology produced no coke and could use less expensive nonmetallurgical coals, characteristics that made it very attractive for town gas production. 

Carbon monoxide and excess steam are normally passed over a cobalt catalyst at about 250-300 C resulting in greater than 99% conversion of CO to COj. This conversion reaction is widely used in oil or solid fuel gasification processes for the production of town gas or substitute natural gas. ... 

Low Temperature Carbonization. Low temperature carbonization, when the process does not exceed 700°C, was mainly developed as a process to supply town gas for lighting purposes as well as to provide a smokeless (devolatilized) soHd fuel for domestic consumption (30). However, the process by-products (tars) were also found to be valuable insofar as they served as feedstocks (qv) for an emerging chemical industry and were also converted to gasolines, heating oils, and lubricants (see Gasoline and OTHER motor fuels Lubrication and lubricants) (31). 

Until the end of World War II, coal tar was the main source of these aromatic chemicals. However, the enormously increased demands by the rapidly expanding plastics and synthetic-fiber industries have greatly outstripped the potential supply from coal carbonization. This situation was exacerbated by the cessation of the manufacture in Europe of town gas from coal in the eady 1970s, a process carried out preponderantly in the continuous vertical retorts (CVRs), which has led to production from petroleum. Over 90% of the world production of aromatic chemicals in the 1990s is derived from the petrochemical industry, whereas coal tar is chiefly a source of anticorrosion coatings, wood preservatives, feedstocks for carbon-black manufacture, and binders for road surfacings and electrodes. 

Until 1960—1970, in countries where natural gas was not available, large amounts of coal were carbonized for the production of town gas, as well as a grade of coke which, although unsuitable for metallurgical use, was satisfactory as a domestic fuel in closed stoves. The early cast-iron and siUca horizontal retorts used at gasworks were replaced by continuous vertical retorts. These operated at flue temperatures of 1000—1100°C. The volatile products were rapidly swept from the retort by the introduction of steam at 10—20% by weight of the coal carbonized. 

Pipelines have a long history. In ancient times, pipelines were used for water transport. Examples are still visible in archeologic areas. However, it is clear that these early constructions could not bear large pressures. The advent of gas pipelines started between 1820 and 1830 with the distribution of town gas. Nowadays pipelines are indispensable in petroleum industries for the transport of various materials, including natural gas, crude oil of various types, and refined products. 

Jones A regenerative process for making carbon black by pyrolyzing petroleum fractions. The gaseous co-product can be added to town gas. 

If the temperature is further increased, e.g., beyond 700 °C, the C2 4 oxygenates further decompose to a mixed gas of moderate heating value, namely to a mixture of CO, C02, H2 and CH4. This gas resembles the town gas that was produced from coal at the beginning of the 20th century. Beyond 1000 °C, the hydrocarbons constituents of the mixed gas are further reformed, which results in the production synthesis gas, a valuable mixture of CO and H2 with some C02 and water as main contaminants. 

Alternatively, tire calorific value may be changed by bringing the components to a new equilibrium at a different temperature. In the Senes A Process, part of the rich gas is further reformed at high temperature and remixed with the remaining rich gas. After water gas shift and partial COj removal a 500 Btu/standard cubic foot product is obtained which is fully interchangeable with the town gas distributed in tire United Kingdom. 

The flow diagram for a rich gas plant producing gas with a calorific value of 710 Biu/slandard cubic foot is shown in Fig. 1. The product is used to enrich lean gas from an IC1 (Imperial Chemical Industries) naphtha reformer which has a calorific value of about 320 Btu/standard cubic foot to the town gas standard of 500 Btu/standard cubic foot (56 Calories/cubic meter). Typical gas analyses arc given in Table 1. 

The Messoyakha gas hydrate field is the first exemplar for gas production from hydrate in the permafrost. Hydrates were produced from this field semicontinu-ously for over 17 years. The field is located in the northeast of western Siberia, close to the junction of the Messoyakha River and the Yenisei River, 250 km west of the town of Norilsk, as shown in Figure 7.29. 

The production of gas sensors. The production records of various types of gas sensors for past five years in Japan are listed in Table I except for the oxygen and humidity sensors. The sensors produced in the largest quantity are of the semiconductive type, followed by the catalytic combustion and thermistor types. These sensors have been mostly applied to domestic uses such as gas leakage alarms or gas control systems for LP gas and town gas which are extensively used for cooking and heating in Japanese houses. This is why these sensors are manufactured on a large scale. Other electrochemical sensors have been developed mainly to monitor other gases. 

Plants in operation/ under construction (products) PRC. NH,. town gas USA. Sag RSA, liquid fuels Great Britain Fuel gas Germany, Austria Fuel gas Germany Syngas Netherlands IGCC (Fuel gas)... 

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