Бурение грунтовых зондов, установка энергетических колодцев

In the dual fluidized-bed (DFB) type design, gasification of the biomass and the combustion of the remaining char occur in two separate chambers as shown Figure 11.3. The biomass enters the first reactor, where it is gasified with steam at 700-900°C, and the synthesis gas produced in the first reactor exits the gasifier with char to a cyclone for gas cleaning. Next, the char separated is transported to the combustion reactor, where it is burnt with air to produce heat. This heat is transported from combustion reactor to gasifier by the circulating bed material. The heat required for heating the biomass and gasification comes from the combustion reactor. The fuel conversion in indirect gasifiers is higher than in CFB — or BFB-type gasifiers (direct gasifiers) because all the char is combusted. The remaining ash contains virtually no carbon, which benefits the overall efficiency of the process. There are two sepa­rate exits for syngas and flue gas. Consequently, dual fluidized — bed (DFB) type designs produce two gases; syngas with little or no nitrogen and a flue gas.

Circulating-type dual fluidized-bed gasifiers (DFB) with steam as the gasification agent have turned out to be a potential technology for large-scale biomass gasification. Steam can be easily produced and facilitate the enhancement of hydrogen content in the syngas [3]. There are a number of advantages in using the DFBG technology.

Some of the important features of DFB gasifiers are:

1. Many forms of biomass samples can be used directly or after minimum pretreatment

2. Easy feeding of biomass

3. Low temperature operation

4. Relatively complex construction and operation

5. Production of syngas with moderate heat value, and moderate tar levels

6. Good cleaning of gas required before use in engines

7. In-bed catalytic conversions possible

8. Good gas-solid contact and mixing

9. Relatively low efficiency

10. Suitable for high specific capacities (>1MW)

11. Good scale-up potential but relatively complex design

The dual fluidized-bed (DFB) type of gasifier is a popular design in biomass gasification. Some major dual fluidized-bed-type bio­mass gasifiers in the world and their locations are summarized in Table 11.2.

Modeling of biomass gasification processes by simulators such as Aspen Plus is a powerful tool to assess mass, energy balances, and to optimize process designs. A model for biomass gasification in

dual fluidized-bed (DFB) reactors by coupling Aspen Plus and ded­icated Fortran has been reported by Abdelouahed et al. [11]. In this study, DFB reactor was divided into three modules according to the main chemical phenomena: biomass pyrolysis, secondary reactions, and char combustion. The calculated compositions of permanent gases, tars, flow rates, and lower heating values were compared with experimental data for two DFB technologies, Tunzini Nessi Equipment Companies (TNEE) and Battelle High Throughput Gasification Process (FERCO). During these studies, Abdelouahed and coworkers found that the syngas composition and flow rate are very sensitive to the water-gas shift reaction (WGSR) kinetics [11].

Комментарии запрещены.