T. Pihu

Calculation of qualitative and quantitative composition of Estonian oil shale and its combustion products. Part 1. Calculation on the basis of heating value

Abstract A method for calculation of the composition of Estonian oil shale and its combustion products is based on the various correlations governing the composition of this oil shale, and relations between its components. To understand better the properties of oil shale and the influence of mining conditions on oil shale quality, a general characterisation of Estonian oil shale is first presented. This unique fuel is utilized for power production, by direct firing in boilers. This paper presents calculations useful for the boiler design engineer for estimating the average characteristics of received oil shale as well as the possible deviations from these mean values. The calculations in this part allow finding the composition of oil shale and the composition of combustion products of oil shale based only upon its heating value. Various considerations in performing oil shale combustion calculation are presented. A calculational example is presented in the appendix of this part. Part 2 of this study extends the method, given the availability of additional fuel analysis data.

Comparison of Ash from PF and CFB Boilers and Behaviour of Ash in Ash Fields

Over 90% of electricity produced in Estonia is made by power plants firing local oil shale and 25% of the boilers are of the circulating fluidised bed (CFB) variety. In 2007 approximately 6.5 million tons of ash was acquired as a byproduct of using oil shale for energy production. Approximately 1.5 million tons of that was ash from CFB boilers. Such ash is deposited in ash fields by means ofhydro ash removal.

Calculation of qualitative and quantitative composition of Estonian oil shale and its combustion products. Part 2. Calculation on the basis of technical analysis data

Abstract A calculational method presented in part 1 is improved on the basis of additional technical analysis data (the heating value, ash content, carbonate content, moisture and sulphur content). The technical analysis data permit calculations of the type presented in part 1 to be carried out for actual samples, and provides the correction coefficients ΔW, ΔCO2m as well as the FeS2 content of the sandy-clay part to be determined. Here are descriptions of two calculations for preparing the data for the basic calculation (see Calculation 1 in part 1). Calculation 2 allows finding the composition of oil shale and its combustion products on basis of technical analysis data for the dry fuel and Calculation 3 using data for as received fuel. In addition, the significance of different elemental composition-based methods for estimating the heating values of the oil shales is explored. This basic input to the calculational model can be influenced by which well-known correlation is employed.

New 215 MWel CFB Power Units for Estonian Oil Shale

Estonian basic power supply is over 90% covered by oil shale fired thermal power plants. Total installed thermal capacity of the boilers is 10.7 GWth and every year about 11 millions tons of oil shale is fired. Two different combustion technologies, the old pulverized oil shale firing and the new CFB technology are used at the moment. The new CFB units totaling 430 MWel delivered by Foster Wheeler Energia started operation in 2003–2004. The very first operational experience of CFB units are very promising and all basic problems of oil shale pulverized firing like high air emissions (SO2 — 820–1360 mg/MJ; NOx — 90–110 mg/MJ), fouling and corrosion of heating surfaces, low efficiency and low operational reliability seemed to be solved. Oil shale CFB firing at much lower temperatures (∼800°C) than pulverized firing (∼1400°C) results only partial decomposition of oil shale contained carbonates, meaning lower specific fuel consumption values and decreased CO2 emissions. Also fly ash composition and properties has been changed, which results in different new prospectives of ash utilization possibilities, but also some additional ash land filling problems. The paper analyses the first data of Estonian oil shale industrial CFB firing in the light of almost 40 year experience of Estonian oil shale use in power production.Copyright

Thermal Effects by Firing Oil Shale Fuel in CFB Boilers

It is well known that during firing of oil shale fuel the amount of heat released during its combustion per kg of fuel is significantly affected by the endothermic and exothermic processes taking place in mineral matter. These thermal effects are calcite and dolomite decomposing, marcasite FeS2 oxidising, CaO sulphation and formation of the new minerals. The given paper deals with the experimental study of the influence of these thermal effects of oil shale fuel having different heating value on total amount of heat released during combustion in calorimetric bomb, circulating fluidized bed (CFB) and pulverized-firing boiler (PFB). The large-scale (250 MWth) experiments were performed in the K11-1 CFB boiler of the Balti Power Plant. During experiments low heating value of a fuel varied within the range 8.5–11 MJ/kg. At the end some conclusions were drawn.