Gas yield

The main difference between gas works and coke oven practice is that, in a gas works, maximum gas yield is a primary consideration whereas in the coke works the quality of the coke is the first consideration. These effects are obtained by choice of a coal feedstock that is suitable to the task. For example, use of lower volatile coals in coke ovens, compared to coals used in gas works, produces lower yields of gas when operating at the same temperatures. In addition, the choice of heating (carbonizing) conditions and the type of retort also play a principal role (10,35). 

In general terms, as the molecular weight of the feedstock is increased, similar operating conditions of hydrogasification lead to decreasing hydrocarbon gas yields, increasing yields of aromatic Hquids, with carbon also appearing as a product. 

Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

Conrad Industries, Inc. (CentraUa, Washington) and Clean Air Products Company (Pordand, Oregon) have jointiy built a tire pyrolysis demonstration machine which allows recovery of combustible gases, oils, and other by-products. The equipment can also handle other carbonaceous material. It is designed to process 0.9 t/h of tires the entire system is estimated to cost about 2.3 x 10 . The feedstock consists of 5-cm tires chips which produce pyrolytic filler, a vapor gas yielding 11.5 kj/m (1000 Btu/ft ), and medium and light oils yielding about 42 MJ/kg (18,000 Btu/lb) (32). 

In the CIS pitch coke is made by carbonizing a hard coke-oven pitch in modified coke ovens. The hard pitch has an R-and-B softening point of 140—150°C and is made by air-blowing a mixture of medium-soft pitch and recycled coking oils. This feedstock is charged in the molten state over a period of 5 h and coked for 17—18 h at 1250—1300°C. The coke yield is 70%. Oils, which are recycled, amount to 20% by weight of the pitch fed. The gas yield... 

Computer Control. The use of computer systems to control the operation of submerged arc furnaces, including calcium carbide, has been successfully demonstrated in the United States (see Expert systems Process control). Operations direcdy under control are mix batching, electrode position and sHp control, carbide gas yield, power control, and cooling water systems. Improvements in energy usage, operating time, and product quaHty are obtained. 

Gas yield, the most impoitant specification for acetylene-giade carbide, is determined by slaking the carbide in water, collecting and measuring the volume... 

Coke Production. Coking coals are mainly selected on the basis of the quaUty and amount of coke that they produce, although gas yield is also considered. About 65—70% of the coal charged is produced as coke. The gas quaUty depends on the coal rank and is a maximum, measured in energy in gas per mass of coal, for coals of about 89 wt % carbon on a dry, mineral matter-free basis, or 30% volatile matter. 

After removal of the unreacted ammonia and recovery of hydrogen cyanide, the waste gas is essentially all hydrogen suitable for other chemical use. The advantages of the BMA process are the high ammonia and natural gas yields and the usehil hydrogen waste gas, but the high investment and maintenance for the converter is a decided disadvantage. 

Blowing agent Class Volatiles produced Decomposition range (°C) Gas yield (cm /g) Comments... 

Azocarbonamide (I) Carbonamide N2, CO, CO2 190-230 220 Most widely used blowing agent in PVC and polyolefins. High decomposition temperature reduced by a variety of metal salts and oxides such as lead carbonate, lead phosphite and zinc oxide. High gas yield. Reaction products show little odour or discoloration. ... 

A popular figure for sludge from average domestic sewage is an expected gas yield of one cuft. per capita per day. Industrial wastes, depending on their character may raise or lower this figure materially. 

The major portion of the digestion with the greatest gas yield is in the primary digester. 

Experiments performed with natural gas yielded somewhat different results. Flames emerged from the confined portion of the apparatus at speeds below 500 m/s, then decelerated rapidly in the unconfined portion with obstacles. On the other hand, flames emerging from the confined portion at speeds above 6(K) m/s continued to propagate at speeds of 500-600 m/s in the obstructed, unconfined portion of the... 

As in hydrocracking, this reaction increases the gas yield and changes the relative equilihrium distrihution of the aromatics in favor of benzene. Table 3-7 shows the properties of feed and products from Chevron Rheiniforming process. 

Dry gas is an undesirable by-product of the FCC unit excessive yields load up the wet gas compressor (WGC) and are often a constraint. The dry gas yield is primarily due to thermal cracking, metals in the feed, and nonselective catalytic cracking. The main factors that contribute to the increase of dry gas are ... 

Feed injection. An improved feed injection system provides optimum atomization and distribution of the feed for rapid mixing and complete vaporization. The benefits of improved feed injection aie reduced coke deposition, reduced dry gas yield, and improved gasoline yield. 

Lower Conversion High Dry Gas Yield Fig. 8-11B Lower Gasoline Yield Figure 8-11C Lower Gasoline Octane Figure 8-1 ID ... 

Dry gas yield is affected by everything that affects conversion (Figure 8-1 IB). Changes to increase conversion can increase the dry gas yield. 

High gas yield shows up as higher speed on the compressor (if centrifugal). In many cases, lower molecular weight (due to higher hydrogen content) can have the same effect. 

Thermal reactions are a function of time and temperature yields are proportional to (time) (exp " ). Figure 9-1 shows the typical elfects of vapor residence time and temperature on dilute phase cracking. For example, at 5 seconds residence time, the dry-gas yield increases 8% when the reactor temperature increases from 960°F to 9S0 "F. increasing the residence time to 10 seconds increases the dry gas yield another 8%. 

On the other hand the Thomas-Fermi method, which treats the electrons around the nucleus as a perfectly homogeneous electron gas, yields a mathematical solution that is universal, meaning that it can be solved once and for all. This feature already represents an improvement over the method which seeks to solve Schrodinger equation for every atom separately. This was one of the features that made people go back to the Thomas-Fermi approach in the hope of... 

Catalytic upgrading of bio-oil was carried out over Ga modified ZSM-5 for the pyrolysis of sawdust in a bubbling fluidized bed reactor. Effect of gas velocity (Uo/U ,f) on the yield of pyrolysis products was investigated. The maximum yield of oil products was found to be about 60% at the Uo/Umf of 4.0. The yield of gas was increased as catalyst added. HZSM-5 shows the larger gas yield than Ga/HZSM-5. When bio-oil was upgraded with HZSM-5 or Ga/HZSM-5, the amount of aromatics in product increased. Product yields over Ga/HZSM-5 shows higher amount of aromatic components such as benzene, toluene, xylene (BTX) than HZSM-5. 

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