Dry-feed gasifiers

The reliability of the dry-feeding gasifier is not as good as the matured CWS feeding system and the initial investment is much higher.39... 

Coals of the Western United States tend to have lower heating values, lower sulfur contents, and higher moisture contents relative to bituminous coals from the Eastern United States. The efficiency loss associated with high-moisture- and ash-content coals is more significant for slurry-feed gasifiers. Consequently, dry-feed gasifiers, such as the Shell gasifier, may be more appropriate for low-quality coals. 

Nitrogen Dioxide. Nitrogen dioxide can be formed in the gasifier from the nitrogen present in the coal. Since N02 is an acid gas, it was included in the study as a potential poison. This study was conducted with C150-1-03 in the electric furnace reactor unit. The catalyst was tested under primary wet gas conditions with up to 8 ppm N02 in the dry feed gas. Table XIV provides a synopsis of the test results. 

British Gas Lurgi Westfield, Scotland 600 TPD/30 MWe Commissioned in 1984 Demonstration unit pressurised dry feed moving bed slagging BGL Gasifier... 

There are three parameters in exponential collocation p N and a characteristic time, At. Different values of p have been used, and no difference has been observed p - 0 was used in the simulations that follow. The number of collocation points (N + 1) is equivalent to the reciprocal of the step size in finite difference methods the more points used, the greater is the accuracy, but the more time consuming the solution. The sensitivity of the solution to N and At is shown in Figure 2, which shows the movement of the combustion zone in an adiabatic dry ash gasifier when the throughput is reduced to 80% of full load at constant feed ratios. 

Biomass dry feed rate to gasifier Biomass moistwe to dyer fiiy basis) Type of dryer... 

Due to the dry feeding of the Shell gasifier, the 02 consumption is reduced, and the efficiency is increased by -2% compared with the CWS feeding system. However, the maximum gasification pressure is limited to about 5 MPa due to the dry-feeding system, as opposed to 8 MPa for some CWS feeding systems. 

The dry-feeding system of the Shell gasifier requires the water content in the bituminous coal to be less than -2 wt %. For high-moisture, low-rank coal, the required water content could be less than 10wt%. 

The dried pulverized coal system is quite complex the nitrogen from dense entrained flow may affect the subsequent chemical process. Thus, the CAPEX is much higher compared with a CWS feeding gasifier for methanol or other coal-to-chemicals plants. 

The feed system is an important choice for entrained-flow gasifiers. GE and E-Gas use a coal-water slurry compared with the dry-feed systems of Shell and Future Energy, which require lock hoppering. 

If these two figures are compared with the coal feeding rate for the LURGI dry-bottom gasifier in line one of Table 1.13 and with the total coal demand in the last line methanol efficiency), it can be seen that the ratio between the total coal demand and the gasifier coal demand is approximately 1.25, i.e. almost the same as the above ratio of 1.18. One may th fore conclude that the simplified look at methanol efficiency is accurate enough to assess different types of coal. 

Run-of-mine lignite is precrushed and screened as required in a coal preparation unit. The particle size of the feed to the dry-bottom gasifiers should not exceed l(X)mm, nor should it fall short of 4 mm to maintain optimum gasifier efficiency. The feed consists of North Dakota lignite with properties as shown in Table 7.1. 

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