Deposit Formation in the FASAN WtE Boiler as a Function of Feedstock Composition and Boiler Operation^†

Abstract

The Danish strategy for waste management is to increase recycling while simultaneously reducing the volume of land-filled waste, in order to avoid loss of resources. An important part of this strategy is waste incineration on a grate, which is a well established thermal treatment technology in Denmark and in several other countries in Europe, North America, and Japan. The method is flexible with respect to operation, allows for recovery of energy, and reduces the volume of solid waste significantly (typically by a factor of 8−10). Furthermore, new and advanced flue gas cleaning technologies ensure very low emissions from modern incineration plants. The presence of inorganic constituents such as alkali metals, Cl, S, and heavy metals is a serious challenge in waste incineration, both with respect to operational [slagging, fouling, and corrosion] and environmental issues. Metals, S, Cl, and ash (oxide species) released or entrained from the grate may cause ash deposition of chemically very aggressive species such as chlorides and sulfates, and thereby promote subsequent corrosion of heat transfer surfaces in the plant. As a consequence, the steam temperatures in superheaters of waste-to-energy (WtE) plants, are usually kept relatively low, that is, in the range 400−430 °C, in order to avoid the excessive corrosion problems usually experienced by deposited alkali and heavy metal chlorides at higher steam temperatures. However, low final steam temperatures means low electrical efficiency of the plant. The present work focuses on deposit formation in the 22 MWth FASAN WtE plant, Næstved, Denmark, with particular focus on the influence of feedstock composition (i.e., firing of different waste types) and operation of the plant on ash deposition. Is it possible to affect deposit amount (i.e., flux of deposit), and chemistry, by playing with the fuel feedstock composition and/or the grate operation? Samples of bottom ash, fly ash, aerosols, deposits, and flue gas were taken while firing different waste fractions or while changing the grate operation (air distribution, oxygen content, length of fire on the grate), respectively. The formation of deposits was then quantified by air-cooled probes, and the chemical analyses of the different deposits were compared and related to the feedstock composition and the operation of the grate, through boiler mass balances. The results indicated that the grate operation may indeed affect the chemical composition and the extent [i.e., the flux (g deposit/area/time)] of deposit formation significantly, whereas the feedstock in the actual campaign did−with shredder waste and PVC as important exceptionsnot differ enough from the base waste fired to cause any serious changes in the extent [flux] and chemistry of the deposit.

Corrosion-Fouling of 316 Stainless Steel and Pure Iron by Hot Oil

“…Eventually, the deposits become thick enough that the furnace tubes must be cleaned or replaced. Similar problems are encountered in a variety of related applications where thick, poorly heat conducting buildups occur and decrease thermal efficiency. − …”

High Efficiency Waste-to-Energy Plants − Effect of Ash Deposit Chemistry on Corrosion at Increased Superheater Temperatures

“…However, the concentrations of these elements in typical waste fuels are often so low that they do not affect the bulk properties of the ash particles, such as melting temperatures, to any large extent. Frandsen et al did not report the content of these or other trace elements in the different waste fuel mixtures, and these elements were not considered in the present study. The compositional inputs for the waste mixtures are given in Table and Table .…”

“…Two sources for the compositional data of the waste fuel mixtures were used. The composition of Na, K, Pb, Zn, Cl, and S were taken from the study of Frandsen et al, where they studied the effect of adding different waste fractions to a reference waste from Danish WtE plants. The additions are salt, shoes, shredder waste, batteries, CCA impregnated wood, and PVC.…”

“…The additions vary between 0.5 and 14.2 wt %. Frandsen et al did not report the concentration of C, H, O, N, or moisture contents of the different waste fuel mixtures. The concentrations of C, H, O, and N and the moisture content of the waste were therefore taken from Becidan et al for a general reference waste (MSW).…”

Role of ZnCl2 in High-Temperature Corrosion in a Bench-Scale Fluidized Bed Firing Simulated Waste Wood Pellets

“…PVC is used in such applications as, e.g., flooring, wallboards, sheeting, and electrical wires. Moreover, Pb- and Zn-containing systems are widely used as PVC stabilizers . Wood surface treatments also contribute to increased levels of Cl.…”