INFLUENCE OF ADDITIVE GRANULOMETRY ON DESULPHURIZATION PROCESS IN BOILERS WITH SUPERPOSED FLUIDIZED REACTOR
Abstract
When fossil fuels are used two main variants as basic coal combustion technologies are applied to steam production such as pulverized coal combustion and fluidized-bed combustion. Pulverized coal combustion finds application for high output boilers. For boilers operating on pulverized coal especially in the field of lower output there is alternative in the form of fluidized-bed boilers.
The main advantage of the fluidized-bed combustion (FBC) is effective control of NOx and SO2 emission during combustion. Relatively undemanding adjustment is needed to set up a system of two-stage fluidized combustion for older boilers by fluidized reactor superposing.
Analysis of flue gas generating during combustion of sulphur-content fuels showed that approximately 99% of whole combustible sulphur creates SO2 and only 0,9 - 1,3% creates SO3 [1].
To fix SO2 in fluidized boilers the most frequently limestone and dolomite are used.
According to the realised tests of potentially suitable additives from 34 localities of the whole Slovak territory practically all Slovak carbonic rocks can be considered as proper additives. The experiments showed that the degree of desulphurization is not only dependent on CaO content, how it was assumed till now, but it is considerably influenced by sum of basic compounds, i.e. CaO and MgO contents. It confirms suitability of dolomite additives, too.
In years 1995-97 there was researched problem dealing with the steam boiler of 40t/h output with superposed fluidized reactor with aim to design the boiler operating system, which treats ecological aspects of sulphur-content fuel combustion.
During experiments 8 sorts of limestone based additives were tried. Reached degree of desulphurization is given in Table 1. The interesting is knowledge that there is relatively long time of SO2 equilibrium concentration setting after adding additives.
The researched investigations confirmed suitability of older boilers adjustment by superposing of fluidized reactor and this way creation of two-stage combustion, dedicated for combustion of Slovak low heat capacity sorts of brown coal. Adding additives of proper granulometry it is possible to fix considerable amount of sulphur from fuel directly into the solid residue of combustion.
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