Analýza podmínek pro spalování čistírenských kalů

Analysis of Requirement for Sewage Sludge Incineration

conference paper

en

Municipal wastewater treatment plants have produced about 160,000 t/y to 210,000 t /y (Eurostat, 2014) of raw sludge (expressed as dry ratio) in the Czech Republic. Considering the calorific value of the dry sludge is about 15 GJ/t, it represents the caloric content in the raw sludge of about 3,000 GJ/y. In many cases, the processing of the separated raw sludge includes the process of anaerobic fermentation, which generates biogas for energy utilization. In the Czech Republic, the produced sludge, mainly digested and dewatered, is used for land reclamation or compost production or it is landfilled. However, the incineration of sludge is a way that is able to significantly eliminate the risks associated with levels of undesirable minor components contained in sludge. Incineration of sludge is a modern technology which is considered as a modern basis in dealing with sludge issues. The calorific value of the raw sludge or product of anaerobic fermentation is significantly reduced to values from 1 to 3 GJ/t due to water content of about 65 to 70 % after mechanical dewatering and late and problematic of mechanical dewatering is summarised. The aim of this paper is to determine under which conditions the sludge incineration process is energy self-sufficient. The paper presents results of a series of balance calculations to determine the optimum rate of drying of raw or anaerobically pre-treated sludge so that the caloric content of the combusted material is sufficient to meet the energy needs of its own technology for energy production intended for export. It is shown that energy production can be significantly affected if the partial drying of the material after mechanical dewatering by waste heat from other operations becomes available. This article builds on the contribution of Fryba (2013) and discusses the conditions of sewage sludge incineration in detail. These are landfilling, energy recovery (incineration, anaerobic digestion, pyrolysis, etc.) or mechanical and biological modifications to minimize the environmental impact. Incineration is an advantageous way of energy recovery. This process utilizes calorific value of sewage sludge and also minimizes the environmental impact. There are more options – incineration in new incineration units specialized on sewage sludge or co-incineration with another primary fuel (e.g. co-incineration with coal in heating or power plants). The objective of the paper is to create models (new sewage sludge incinerator and coal-fired power plant, where is incineration sludge with coal) to detection amount of emissions. Emissions are compared with European emission limits for waste incineration plants. The goal of the research is evaluation of the two mentioned ways of sewage sludge incineration from emission production point of view. Results are then compared with European limits on emissions from waste-to-energy plants. Further, modifications in flue gas cleaning system are proposed to meet the limits and costs on these modifications are performed.

V České republice je v čístírnách komunálních odpadních vod ročně produkováno asi 170 až 210 tis. tun surového kalu (vyjádřeno jako suchý podíl). Při výhřevnosti suchého podílu zhruba 15 GJ/t představuje kalorický obsah v surovém kalu asi 3000 GJ/r. V řadě případů zpracování separovaného surového kalu zahrnuje proces anaerobní fermentace, při kterém vzniká energeticky využitelný bioplyn. V ČR se produkované kaly, převážně vyhnilé a odvodněné, používají k rekultivacím, k výrobě kompostů nebo se skládkují. Nicméně spalování kalů je způsobem, který je schopen výrazně eliminovat rizika spojená s obsahem nežádoucích minoritních složek obsažených v kalech a proto je technologie spalování kalů považována za moderní východisko při řešení kalové otázky. Kalorická hodnota surového kalu nebo produktu anaerobní fermentace je však výrazně snížena na hodnoty cca 1 až 3 GJ/t v důsledku obsahu asi 65 až 70 % vody po mechanickém odvodnění. Záměrem příspěvku je stanovit, za jakých podmínek může být spalování kalů energeticky soběstačný proces. Příspěvek bude prezentovat výsledky řady bilančních výpočtů s cílem určit optimální stupeň vysušení surového nebo anaerobně předupraveného kalu tak, aby kalorický obsah spalovaného materiálu byl dostačující pro krytí energetických potřeb vlastní technologie pro produkci energie určené na export. Je ukázáno, že výrobu energie je možné významně ovlivnit, pokud k částečnému vysušení materiálu po mechanickém odvodnění bude k dispozici odpadní teplo z jiných provozů.

Municipal wastewater treatment plants have produced about 160,000 t/y to 210,000 t /y (Eurostat, 2014) of raw sludge (expressed as dry ratio) in the Czech Republic. Considering the calorific value of the dry sludge is about 15 GJ/t, it represents the caloric content in the raw sludge of about 3,000 GJ/y. In many cases, the processing of the separated raw sludge includes the process of anaerobic fermentation, which generates biogas for energy utilization. In the Czech Republic, the produced sludge, mainly digested and dewatered, is used for land reclamation or compost production or it is landfilled. However, the incineration of sludge is a way that is able to significantly eliminate the risks associated with levels of undesirable minor components contained in sludge. Incineration of sludge is a modern technology which is considered as a modern basis in dealing with sludge issues. The calorific value of the raw sludge or product of anaerobic fermentation is significantly reduced to values from 1 to 3 GJ/t due to water content of about 65 to 70 % after mechanical dewatering and late and problematic of mechanical dewatering is summarised. The aim of this paper is to determine under which conditions the sludge incineration process is energy self-sufficient. The paper presents results of a series of balance calculations to determine the optimum rate of drying of raw or anaerobically pre-treated sludge so that the caloric content of the combusted material is sufficient to meet the energy needs of its own technology for energy production intended for export. It is shown that energy production can be significantly affected if the partial drying of the material after mechanical dewatering by waste heat from other operations becomes available. This article builds on the contribution of Fryba (2013) and discusses the conditions of sewage sludge incineration in detail. These are landfilling, energy recovery (incineration, anaerobic digestion, pyrolysis, etc.) or mechanical and biological modifications to minimize the environmental impact. Incineration is an advantageous way of energy recovery. This process utilizes calorific value of sewage sludge and also minimizes the environmental impact. There are more options – incineration in new incineration units specialized on sewage sludge or co-incineration with another primary fuel (e.g. co-incineration with coal in heating or power plants). The objective of the paper is to create models (new sewage sludge incinerator and coal-fired power plant, where is incineration sludge with coal) to detection amount of emissions. Emissions are compared with European emission limits for waste incineration plants. The goal of the research is evaluation of the two mentioned ways of sewage sludge incineration from emission production point of view. Results are then compared with European limits on emissions from waste-to-energy plants. Further, modifications in flue gas cleaning system are proposed to meet the limits and costs on these modifications are performed.

kal z čistíren odpadních vod, emise

sewage sludge, emission

2014

23.08.2014

AIDIC Servizi S.r.l.

Milano, Italy

978-88-95608-30-3

2283-9216

Proceedings of the 17th CONFERENCE ON PROCESS INTEGRATION, MODELLING AND OPTIMISATION FOR ENERGY SAVING AND POLLUTION REDUCTION PRES 2014

39

631–636

6