Dense‐phase feeding of pulverized coal in uniform plug flow

Abstract

A series of high-pressure pneumatic dense-phase flow experiments were conducted using pulverized coal as the granular solids. This granular material was transported by nitrogen gas out of a conical feeder tank, through a length of stainless-steel tubing and into a pressurized receiver tank. Only the nitrogen gas trapped in the interstices of the coal particles inside the feeder tank was used to transport the coal. Six different transport stainlesssteel tube geometries were used.A detailed analysis of the system is performed. This analysis reasonably predicts the expected solids flow rate for a given set of operating conditions and the minimum pressure drop required to maintain flow. K. M. SPROUSE SCOPEPneumatic conveying of pulverized solids is an extremely interesting field of study. Many different types of transport systems have been developed for commercial use as described by Kraus (1980). Perhaps the most reliable technique for conveying bulk materials is the dilute-phase transport method which mechanically feeds granular solids into a high-velocity gas stream. This highly turbulent gas stream rapidly entrains the particles and prevents them from settling out as the solids are transported over a given distance.Dilute-phase transport is characterized to a great degree by extremely high gas to solids volume conveying ratios and low gas pressure drops. For many applications, these high volume ratios are not desirable due to restrictions on feed system size, gas compressor or blower power requirements, or the amount of carrier gas allowed for conveying. In response to these restrictions, commercial systems are now available which significantly reduce the gas to solids volume ratio. The trade-off that occurs by reducing the transport volume ratio is that the gas pressure drop across the feed line is significantly raised, and since the solid particles are in much closer contact with one another, the chances of plugging the feed line are greatly increased. Wen and O'Brien (1976) and Klinzing (1981) have reviewed the types of analyses and experimental studies which have been used in designing both dilutephase transport systems and those using lower gas to solids volume ratios. They have indicated that by lowering the volume ratio, a flow condition will be reached whereby the solids will begin to separate out from the main gas stream and flow in a nonuniform condition. This flow regime has been defined as dense-phase solids transport. However, once the volume ratio has been reduced to the point where the entire transport line is filled with granular material at or near its static bed void fraction, Wen and OBrien (1976) and Klinzing (1981) indicate that the pipe will plug, thus terminating flow.Experimental efforts by Burge et al. this is not necessarily true with proper feed system design. Reliable dense-phase feeding in uniform plug flow can be maintained by keeping inside pipe walls smooth with no sudden cross-sectional area contractions or expansions and by providing sufficient gas pressure drop through the f...

Linear Extrusion 400 Tons/Day Dry Solids Pump

“…The model used in determining performance of the linear extrusion dry solids pump was taken from Schuman (1983 and1986). For a linear dry solids extrusion pump with relatively slow moving walls, the inertial terms in the momentum equations can be removed ~ which greatly simplify the remaining equations to be solved.…”

“…If one were modeling the Lockheed kinetic extruder pump, Meyer et al (1983), these terms would need to be retained within the model. The solids constitutive relations used in the linear dry solids extrusion model are found in the "Solids Stress Tensor" Supplementary Materials Section of Sprouse and Schuman (1983) -which can be obtained directly from the AlChE Journal, New York, for a nominal fee).…”

“…The effective particle size is also a function of the tortuosity and particle shape within the solids bed. Sprouse and Schuman (1983) reported that the effective particle size D p for use in the above relations is the volumediameter mean, D31, of the nominal particle size distribution. Perry and Chilton (1973) recommends use of the Sauter mean diameter, D32, for determination of the gas permeability coefficient.…”

“…In addition to extrusion pump modeling with the continuum mechanics approach of Schuman (1983 and1986), the developing field of granular dynamics (GD) --see, e.g., Theuerkauf et al (2007) --may someday also be a viable modeling alternative. Limitations with this method -for extrusion pumps feeding standard industrial grind size particles (whose basic building blocks are nominal 8-|im size spheres) ~ are the billions of particles required to be tracked during the computation.…”

Dry Coal Feed System and Multi-Element Injector Test Plan

“…Pratt & Whitney Rocketdyne (PWR -a United Technologies Company) started the development work on these feed system in the 1970's -see, e.g., Oberg and Hood (1980) and Sprouse and Schuman (1983). These pulverized coal feed systems were successfully demonstrated on a number of U.S. Department of Energy (DOE) and company funded test programs to pressures of 1,500 psia and coal flow rates of approximately 50 tons/day.…”