دانلود رایگان ترجمه مقاله تاثیر لجن فاضلاب بر خصوصیات رئولوژیکی دوغاب زغال سنگ – آب (نشریه الزویر ۲۰۱۰)

اثرات لجن فاضلاب بر ویژگی های رئولوژیکی دوغاب زغال سنگ-آب

Effects of sewage sludge on rheological characteristics of coal–water slurry

Abstract

The coal–sludge slurry (CSS) containing coal, sewage sludge and water was prepared to study the effects of sewage sludge on rheological characteristics of the CSS. The yield stress, thixotropy and rheological type of CSS were investigated and compared with those of coal–water slurry (CWS). The results showed that the yield stress of CSS appears at the shear rate range from 0.05 to 0.14 s−۱٫ For CSS with the naphthalene sulfonate sodium formaldehyde condensate as dispersant and the sludge/coal mass ratio of 10:100, the yield stress can reach to 22.9 Pa. The thixotropy was quantitatively described by the thixotropy loop area, and sewage sludge can obviously improve the CWS thixotropy. The non-Newtonian behavior of CSS was characterized by a progressive decrease in viscosity with increasing shear rate at the shear rate range from 5 to 180 s−۱٫ By the analysis of FTIR, SEM and optical microscope, hydrophilic functional groups and colloidal structure of sewage sludge play the key roles on the different rheological characteristics of CSS and CWS.دوغاب زغال سنگ-لجن، تبخیرشدگی-همزمان، ویژگی های رئولوژیکی، FTIR

۱ Introduction

Since energy and environmental protection become an important global issue, the efficient utilization of coal can play a very vital role on future energy policy. Coal–water slurry (CWS) [1,2] gasification as clean coal technology is an important method to tackle energy maintenance and developmental problem in the 21st century. One of the problems concerned is the stable feeding of CWS to the gasifier. During the past 20 years, feedstock technique of pumping CWS has been the focus of attention by energy researches in many countries [3–۵]. The slurry is transported over long distances of several hundred kilometers, which creates severe problems such as settling of solids, wear of the conduit by erosion, and huge power requirements for the whole transport process [6]. Therefore, a detailed understanding of the rheological characteristics of CWS is a prerequisite for its optimum and safe processing. CWS is a complex and high concentrated suspension (solid mass content usually =60 wt.%) mixed with water and coal powders. Many authors concluded that the rheological characteristics of CWS would be varied with coal content, coal particle size distribution and additives, etc. [7–۱۰].

A new sewage sludge disposal method is to prepare coal–sludge slurry (CSS), which could instead of coal–water slurry (CWS) in the entrained-flow gasifier to realize the co-gasification of sewage sludge and coal [11]. The coal–sludge slurry is prepared by mixing the sewage sludge, coal powders, water and dispersant. This process does not require pre-dried sewage sludge because a certain quantity of water is needed during CWS gasification. In the process of co-gasification, the water and calorific value of sewage sludge can be adequately utilized. Sewage sludge addition to CWS forms a ternary mixture, which is composed of rigid coal particles, deformable sewage sludge and flowing water. The rheological characteristics of CSS become different to those of CWS, and are also of special significance. In this paper, several kinds of CSS and CWS were prepared. The rheological characteristics of CSS were investigated by Malvern Bohlin CVO rotating-type rheometer, and compared with those of CWS.