Characteristics of coal ash and their role in hydraulic design of ash disposal pipelines

Abstract

Th e hydrauli c des ign of ash di sposa l pipelines is strong ly dependent on th e properties of as h as well as th e rh eo logica l behav iour of th e ash slurrie s. The va ri ous so lid properti es of Il y as h and bed as h co ll ec ted from di ffe rent power pl ant s sp read across th e country have becn in ves ti ga ted. Furth er, the rh eo log ical beh av iour of th e va ri ous sa mples has bee n qu anti­ li ed ove r a wid e range of solid co ncent rat ion. Th e prese nt in ves ti ga tion s sho w th at th e properti es of differe nt as h sa mpl cs (both Ily as h and bed as h) vary ove r a wide ran ge . Similarly, th e rh eological parameters (yield str ess and relativ e visc osit y) of th e slu rries at different concent rations ex hibit a wide varia ti on. Thus, th e design of as h di sposa l pip elin e has to take into account th e wid e va ri atio n in so me of th e rh eo logical para meters in ord er to opt imi se th e energy and water co nsum pt ion. Power generation in India is, at present , primaril y coal based . It is expec ted th at India alone will be producing approximate ly 100 milli on tonnes of ash by th e turn of the century. At present, bulk of th e ash is bein g transported by slurry pipe lin es fr om the thermal powe r pl ant s to as h ponds, spread over large areas in th e vicinity o r th e plants. Currently, th e desi gn of th e ash di sposal pipelin es is based on the criteria of reliabi lit y with littl e or no emphasis on th e optimisation of th e va riou s paramete rs lik e water and th e energy co nsumpt ion, eco nomi c consid erations , etc. The present design procedure. result in excessive wastage of both water and energy. It has become imperative to optimi se th e des ign meth odolo gy of th ese pipelines as th is is go in g to re ma in th e pri mary meth od for disposa l of ash for years to come. He nce, it is import an t to ha ve basic know ledge about th e mechani sm of tran spo rtat ion . In ord er to op timi se th e mechani sm of tran sportati on sys tem, a detail ed knowledge of th e characteri sti cs of fl y as h and bed as h slurri es be in g produ ced in th e count ry is essenti al. This stud y aims to generate dat a on th e properti es of fl y ash and bed ash, and their lurri es over a wid e range of so lid concent rat ion so as to establi sh the feas ibilit y of transport ing as h at higher concentrati on. The bas ic parameters for th e des ign of any slurry pipelin e are the hydrau li c para meters whi c h in clu de pro perties o/ carri e r fluid , optimum partic le s ize, optimum solid concentrati on in th e slurr y, rheology of the slurry, specifi c grav it y of so lids, etc . Rh eology of