Shoichi Takao

The Effects of Agitation on the Rheology of a Coal Water Mixture

The changes in CWM rheological properties by means of high speed agitation were investigated through batch agitation tests using a laboratory-scale agitator. In this study, the rheological properties were measured according to the CWM Quality Test Method, (Center for Coal Utilization, JAPAN United Method). It was found possible to decrease the apparent viscosity of a CWM and improve the statical stability by agitation. The decrease in the apparent viscosity is mainly attributable to the more uniform dispersion of dispersant promoted by high shear agitation. The improvement of statical stability is mainly attributable to the increase in the structural viscosity caused by clay minerals liberated from the coal surface during agitation.

Study on Statical Stability of a CWM.

(財) 石炭利用総合センターのCWM品質試験法に準じて, CWMの静置安定性評価試験を行った.静置期間の経過に伴い石炭粒子の沈降と凝集によってハードパックとソフトパックが増加した.CWMの代表粘度が高いほど静置後のハードパックが増加し, 逆にハードパックの石炭濃度の上昇は小さくなる傾向がみられた.CWMの初期の代表粘度, レオグラムのヒステリシスループの面積および粘度指数などのレオロジー特性から, 静置後のハードパックの量と石炭濃度を概ね予測できることが明らかになった.また静置期間中に定的期に攪拌することによってハードパック量を大幅に低減できた.

Study on a CWM preparation system.

In order to develop a preparation system of a highly loaded coal water mixture (CWM) a bench scale test, a pilot scale test and a demonstration test were conducted, where a high concentration wet grinding method was employed.CWM prepared by the high concentration wet grinding method contains desirable quantity of fine particles which are needed for ensuring lower viscosity at high concentrations and also for good statical stability. One of the major subjects of this grinding method is how to decrease coarse particles over 150μm because the coarse particles tend to become unburned carbon when CWM is burned.In the grinding tests, it was found that the increases of the length/diameter ratio (L/D) and the number of compartments of mill were both effective to decrease coarse particles. A two-stage grinding method was also effective. Based on these findings, an 1-stage feed and 2-stage grinding system using multi-chambered long tube mills was developed.In the demonstration test with a capacity of 26t/h, a CWM prepared by this system was found to contain a very little amounts of coarse particle with good rheological properties. The statical stability and the combustibility were also found satisfactory.