Svaveldosering i fastbränslepanna

Sammanfattning

At the SCA papermill in Obbola byproducts from the pulp- and paper production are incinerated together with purchased wood fuels to produce steam in Ångcentral 2 (Steam centre 2). As the boiler was built for other types of fuel there are currently problems with both emissions and corrosion. Earlier studies, on other boilers, indicate that dosing sulphur could help solve some of these issues. This thesis aims to investigate the effects on emission and, as far as possible, also corrosion and efficiency of the boiler, of dosing granulated sulphur to the solid fuel in Ångcentral 2. The thesis consists of a literature study, tests with sulphur dosing at three different concentrations as well as tests with reduced oxygen flow to the combustion. The results shows that variations in production and fuel have a large effect on which changes can be noted, the large standard deviation in the measured values also makes the changes less distinct. To summarize, some reduction in carbon monoxide emissions (CO) can be noted. The emissions of nitrous oxides (NOx) are not reduced by the sulphur dosing but rather increase slightly and the tests with reduced oxygen flow resulted in too unstable production too be a realistic alternative, the oxygen reduction also resulted in large increases in the CO emissions. The emissions of hydrogen chloride (HCl) seem to increase which could indicate a decrease in corrosion caused by chloralkaline compounds. The emissions of sulphur dioxide noticeably increase, especially at higher sulphur concentrations, which was expected but which could result in increased low temperature corrosion. The efficiency looks to be increasing slightly at high dosing concentrations but with very high standard deviation for these measurements it is difficult to evaluate the actual effects. The conclusion drawn from the tests at Ångcentral 2 is that the desired effect on the Nox emissions is missing and that the effect on corrosion in the boiler is difficult to evaluate. Depending on how the increase in NOx is delt with, production using sulphur dosing might be more expensive, due to these reasons sulphur dosing was determined to not be a good match for this boiler.