No abstract

The paper presents method of calculation of the heat leakage and efficiency by using method of indirect heat balance, utilizing data from gas analysis, which can be employed for operational evaluation plant operation during burning of different types of waste materials. Taking into account that practically only oxygen and carbon dioxide is being measured in the exhaust gases, calculation method for heat leakage with exhaust gases, using measurements of only this component, without utilizing carbon dioxide content in combustion products, was developed. Carbon dioxide and oxygen calculated percentage content in dry complete combustion products in actual air consumption was measured with consideration of incomplete combustion. Heat leakage for low power boilers and furnaces was analyzed, heat leakage calculation method for this kind of plants was introduced. Using design factors analysis of the solid fuel boilers for burning low-calorie fuel and wood waste, was developed dependence of the outside walls specific area of the boiler on the boiler’s efficiency. Based on the developed method for seven types of the RDF fuels, tabular and graphic dependences for reduced factors, characterizing heat leakage to the atmosphere and incomplete combustion, were introduced. Suggested method was tested for calculating losses in solid fuel water heating boiler with grate stoker and designed output power of 200 kW during burning of the briquetted waste materials.

Objective of this paper is an analysis of briquetted waste combustion in the low power boilers. Research was conducted for the 100 kW pyrolysis heating boiler and 200 kW heating boiler with grate stoker. Briquettes were made by compacting milled and crushed materials into cylinders 50 mm in diameter, with a length of 100-200 mm, density of 800 kg/M3. It was established that process of combustion in low power boilers has low thermal efficiency, value of which fluctuated within 60…74% for wood combustion and 50…70% for RDF briquettes combustion. Burning process was stable and characteristics of the RDF combustion were similar to the wood combustion. Incineration of the fuel briquettes had better effectiveness than burning of solid wood. During RDF briquettes combustion high CO content (up to 0,2% or 2000 ppm) in flue gas was observed, which is an indication of insufficient burning time. It may be concluded that waste incineration in low-duty plants is viable, but to secure complete combustion and desired temperatures process of combustion and heat extraction should be separate in terms of design.

The paper suggested the calculation method of combustion for solid and gaseous fuel cofiring. The calculation is suggested to carry out for per unit of generated during combustion total capacity instead of per unit of weight or volume of fuel. This method was tested during combustion parameters examination at cofiring of solid municipal waste, which is the main fuel, and landfill gas (biogas) which is the additional fuel for thermal mode stabilization. The calculation has been conducted for waste with the moisture content of 50%, 30% и 10%, which are solid fuel, methane, as a reference fuel, common biogas with a methane content of 60%, and biogas with a low methane content of 35%. It was established that additional input of biogas is effective for the combustion of unprepared waste with high moisture content, moreover, it is possible to use common biogas as well as biogas with low methane content. The required combustion product temperature (900-1000°C) for unprepared waste can be achieved at the excess air coefficient of 116 or more. In summary, solid fuel and biogas cofiring allows operative control of the combustion process and sustain combustion product temperature and heat output of units at a constant level. The combustion process regulation should be based on the given temperature of combustion products by changing two parameters: landfill gas flow rate and flow rate of air supplied for combustion.

Content evaluation of the hazardous substance emission from different types of waste combustion in two solid-fuel water heating boilers was carried out. For 100 kW pyrolysis boiler the content in exhaust gases of the following compounds was determined: NO2, NO, CO, CH4, phenol, benzol, SO2, formaldehyde, HCl. For 200 kW stoker grate boiler the content in the exhaust gases of the following compounds was determined: CO, NO2, NH3, mercaptans, H2S, phenol. For the targeted factors, the calculated hazardous substance ground-level concentrations don’t exceed the maximum allowable concentration limit. The hazardous substance emissions in low power boilers are comparable with high power analogs but have lower combustible efficiency. Waste combustion in the pyrolysis boilers creates 2-10 times less hazardous substances than in grate firing. It was established that combustion mode influences only the carbon monoxide content. The content of other hazardous compounds in the exhaust gases doesn’t depend on the combustion parameters. The additive criterion of total emissions was suggested, which presents the sum of the ratio of the calculated ground-level hazardous substance concentrations to maximum allowable concentrations. Unlike the existing dimensionless concentration, the criterion considers hazard class and compound fraction in gases. The highest criterion value of the total emissions was noted during wood waste combustion (windows, doors, furniture) and RDF fuel, which contains a large amount of plastics