دانلود رایگان ترجمه مقاله احتراق لجن فاضلاب و پودر زغال سنگ (نشریه Ijesd 2014)

احتراق لجن فاضلاب و پودر زغال سنگ

Combustion of Sewage Sludge and Coal Powder

Abstract

The technology to facilitate liquid sewage sludge disposal with minimum energy consumption for primary drying before incineration in a furnace is proposed. The possibility to use an industrial boiler was studied experimentally. The experimental test-rig was developed at Technion (Israel Institute of Technology) and the proposed concept was demonstrated successfully. Sewage sludge from municipal wastewater plants with a moisture content of up to 95-99% combined with pulverized coal and liquid light fuel at various ratios was burnt. Sewage sludge co-combustion leads to an insignificant temperature reduction inside the furnace, and is able to provide stable combustion with low NOx and CO emissions.

1 Introduction

The objective of the present study was to burn liquid sewage sludge disposal by furnace incineration without preliminary desiccation as this requires additional energy consumption [1], [2].

The annual USA and Europe market for sludge environmental services is over 16 million tons of sewage sludge (dry mass), according to world industry sources estimation [3]. This market is expected to grow in parallel with wastewater treatment and reuse increase. Recently, the amount of wastewater processed in sewage treatment plants (STP) has increased annually by ~ 3% [4]. Most of these plants include biological treatment. The disposal of sewage sludge from urban wastewater treatment plants became an important issue due to the prerequisite to minimize its environmental pollution impact. Since land-filling is not a suitable solution according to environmental point of view, a thermal treatment process proved to be the most appropriate solution. Combustion of sewage sludge mixed with coal, in a conventional incinerator system is an attractive alternative that provides partial compensation for sludge disposal cost and concurrent energy production.

Sludge combustion provides an amalgamation of several advantages which cannot be found in other alternative treatments. Among these advantages, a highly significant reduction in volume (to ash) and cost reduction of sludge process. The resulting dry ash accounts for 10% of the initial volume and it is free from toxic organic constituents that were burnt off [5]. Furthermore, the calorific value of the dry sludge corresponds to that of brown coal and it may be recovered through combustion [6].

In the last few years, utilities have become interested in co-firing biofuels with coal and other fossil fuels, applying wood wastes and other solid forms of biomass to increase of capacity of power generating plants [7]-[11]. Initially, co-firing has been considered as a mean to reduce greenhouse gas emissions from fossil energy generation operations. Biomass co-firing with coal proved to be the most inexpensive method to generate green power in a utility plant [7], [12]-[17]. Also from the economic point of view prospect of the joint combustion of sludge and coal in power plants can be an attractive option since it allows the use of existing infrastructures, which are already equipped with the appropriate devices for flue gaseous emission control [18]. Furthermore, in near future new regulations will highly restrict the actual disposal procedure of municipal sewage sludge. Based on soil and groundwater protection, sterner requirements will have to be met in regard to pollution level of sewage sludge, limiting its use as fertilizer [19].

In the present study liquid sewage sludge was burnt in a furnace without preliminary desiccation and its joint combustion with light fuel and pulverized coal has been investigated under laboratory conditions. The novelty of the present research is the availability co-firing of liquid sludge with other fuels that has not yet been determined.