US2659449A - Humidifying system for dust and fume collection by electrical precipitation - Google Patents

Description

Nov. 17, 1953 H. E. KAISER ETAL v 2,659,449. HUMIDIF'YING SYSTEM FOR DUST AND FUME COLLECTION BY ELECTRICAL PRECIPITATION Filed April 5, 1950 I ATER 19 SPRAY q z i TEMPERING AIR F 29 KILN END FA 85 K ILN HOUSING PRECIPITATOR 21 27 PRESSURE EQUALI 2! N6 Patented Nov. 17, 1953 HUMIDIFYING SYSTE FUME COLLECTION CIPITATION Harry E. Kaiser,

fornia. Portland Colton,

bell, San Bernardino, C Cement Calif., a corporation of C M FOR DUST AND BY ELECTRICAL PRE- and William 0. Campalif., assignors to Cali- Company, alifornia Los Angeles,

Application April 3, 1950, Serial N 0. 153,57 6

6 Claims.

This invention has to do with improved methfor effecting maximum separation, by elecprecipitation, of contaminants from gas streams while benefiting generally the separation system and equipment, and is directed particularly to such separation from high temperature gases of contaminants including dirt and dust particles, as well as fume resulting from vaporization or sublimation of compounds and elements of essentially mineral or inorganic nature. While applicable to the improvement of electrical precipitation systems for cleaning high temperature gases of various compositions and Origins, the invention has been developed with one particular objective, among others, of removing dust and fume from Portland cement kiln gases, and accordingly will be described with reference to that typical adaptation.

The customary methods for separation of dust and fume from the kiln gases before their release to the atmosphere are the so-called wet and dry systems, the former utilizing relatively great quantities of water for separation incorfrom gases that may have controlled humidification.

In a conventional dry separation system, hot gases (at a temperature e. g. in excess of 1'000 F.) are taken from the kiln through an outlet duct containing a fan or blower, and discharged through an electrical precipitator, say the well known Cottrell precipitator employed for the separation of dusts and fumes. It has been necessary to cool the hot gases ahead of the precipitator, and particularly ahead of the fan, since the latter cannot withstand the gas heat at or near the kiln outlet temperatures. A-

and precipitator. Such induction of air ordinarily adds considerably to the gas volume finally discharged into the atmosphere.

Also, ordinarily required for most eflicient operation of the precipitator, and particularly with respect to fume removal, is controlled humidification of the gas stream going to the precipitator. The usual expedient has been to spray water into the gas stream between the kiln and precipitator and in quantities required for the necessary gas humidification. One very objectionable result of this practice is the accumulation of large quantities of muds and slurries in the water spray chambers, and the problems incident to disposal of the mud.

By the present invention it is now made possible to obviate these objectionable aspects of the conventional methods, by providing essentially a truly dry system, capable nevertheless of the required gas humidification, which results in a reduced gas volume release to the atmosphere, and substantially complete elimination of mud or slurry accumulations.

According to the present system, the kiln gases carrying separable dust particles and fume are discharged to an electrical precipitator by a fan or blower in an interconnecting duct which may or may not also contain in advance of or beyond the fan, a mechanical dust separator,

for example of the cyclone type. One portion of the clean gases leaving the precipitator is discharged to the plant stack, while a second portion of the clean gases is recirculated through a return duct into the clean gas stream at a point in advance of the fan, the kiln end housing. Humidification of the gases going to the precipitator, and to a degree required for its most efficient operation particularly with respect to fume removal, is accomplished by the introduction of moisture to the recirculated gases, preferably within the return duct as by means of a spray chamber. Being introduced into the clean gases containing minor or inconsequential solids, the injected water can produce no consequential mud or slurry formation, thus obviating the objectionable mud accumulations in the conventional systems as previous outlined. Thus while having sufiicient moisture content to humidify and cool the kiln discharge gases to the required extent, the recirculated gas stream contains no liquid moisture tending to wet and form mud accumulations or solids in the kiln-precipitator duct. Consequently, the system operates essentially dry.

All of the various features and objects of the invention, as well as the details of certain illustrative embodiments, will be understood more fully from the following description of the accompanying drawing, in which:

Fig. 1 is a view illustrating diagrammatically an electrical precipitation and humidifying system operating in conjunction with a single kiln; and

Fig. 2 is a similar view showing the applicability of the invention to the operation of multiple kilns employing clean gas recirculation in a corresponding number of precipitators to a single pressure equalizing chamber.

Referring to Fig. 1, hot gases carrying separain the Portland cement clinkering kiln W are discharged through the kiln end blower l2 through duct l3 into the electrical precipitator H, e. g. a Cottrell precipitator. The latter operates to separate practically all dust from the gases and at least a major portion of their fume content. Leaving the precipitator, a portion of the clean gases flows through duct l5 to the stack IS.

A second portion of the clean gases discharged from the precipitator, and in an amount con trollable as by means of a damper I! in duct i5, is recirculated back into the kiln hot gas stream through a return duct IS. The latter contains a fan or blower l9 which displaces the gases through a humidifying zone 20 which may consist of a spray chamber into which water is introduced in finely divided form to become completely vaporized in the gas stream. The quantity of water introduced to the spray chamber may be so controlled that when introduced to the kiln gas stream, the recirculated gases will raise the humidity of the gaseous mixture fed to the precipitator, to within the range required for most eflicient operation of the precipitator, and particularly with respect to its fume removing capacity. Preferably, the recirculated gas is introduced through duct 18 into the kiln end housing H and in advance of the fan 12 in order to cool the kiln gases below temperatures injurious to the fan.

The following flow rates, temperatures, humidities and so forth may be cited as typical operating conditions applicable to the described separation and recirculation system. In a typical instance hot gases containing about 16.5% Water may be assumed to flow from the kiln at the rate of 68,000 C. F. M. (cubic feet per minute) and at a temperature of 1500 F. Including the recirculated gas stream, the gases flow through duct l3 to the precipitator at a rate of 101,000 C. F. M. at 660 F., as a result of humidification by the recirculated streams the gases fed to the precipitator have a water content of about 22.9%. That portion of the clean gases discharged to the atmosphere through the stack l6 may amount to about 53,000 C. F. M. at 620 with moisture content of 22.9%. A second portion of the gases at this same temperature and humidity may be recirculated into duct is at the rate of around 44,800 C. F. M. Introduction of water to the spray chamber 20 at the rate of around 14% gallons per minute produces a gas stream recirculated into the kiln end housing at the rate of about 33,200 C. F. M. at a temperature of around 250 F., the water content of this stream being about 32%.

While it is to be understood that complete cooling of the hot kiln gases to the extent required, may be accomplished by means of the recirculated and humidified gases, if desired some atmospheric cooling or tempering air may be admitted to the kiln gas stream as through line 20 leading into the kiln end housing. Merely as illustrative, under the particular operating conditions assumed in the foregoing, 80 F. atmospheric air may be introduced to the kiln end at the rate of around 4,700 C. F. M.

Fig. 2 illustrates a variational embodiment of the invention directed particularly to the separation and recirculation of gases by essentially the procedure described with reference to Fig. 1,

and precipitator system. Here the kilns and end housings 2 I, 22 and 23, 24 are discharged by fans 25 and 26 through ducts 21, 28 to the precipitators 29 and 30. Portions of the clean gas streams leaving the precipitators are discharged through interconnecting duct 3| to the stack 32. The remaining clean gases are recirculated by fans 33 and 34 through ducts 35 and 36 to the spray chambers 31 and 38. The humidified gas streams flow from the spray chambers to a common pressure equalizer chamber 39 which preferably is vented to the atmosphere. The mixed gas streams thence are taken through duct 40 for delivery into the kiln gas streams going to the precipitator. In Fig. 2 we have illustrated dampers 4| at various locations in the system for regulation of the proportions of the gas streams to be recirculated and the proportions to be returned to the kiln gas streams, these dampers also being so located as to permit isolation of all or any part of each kiln, precipitator and spray chamber system from the other.

If for any reason either recirculation fan or spray chamber should cease to function properly, the volume of humidified gas being returned through the other recirculation duct may be increased to adequately serve to cool and humidity the streams going to both precipitators, and with or without the addition of tempering air. On the other hand, should the recirculation gas requirement for either kiln and precipitator system be interrupted, then all excessive amounts of gas being returned through both recirculation systems, may be vented to the atmosphere from the pressure equalizing chamber 39.

Speaking generally of the operating conditions to be maintained in the described systems, the rate of the clean gas recirculation, its temperature and humidity, will be regulated to reduce the hot gas stream temperature well below 1000 F., and preferably below 700 F., and to increase the humidity of the mixture going to the electrical precipitator as required for its most efficient operation. Ordinarily, the addition of moisture by way of the recirculated gases will be governed to maintain the water content of the gases passing through the precipitator between about 15% to 30% by volume of the gas.

We claim:

1. In the operation of 9. Portland cement plant comprising a plurality of clinkering kilns each communicating with its individual electrical precipitator, the method that includes passing a stream of hot gas from each kiln through an electrical precipitator operating to remove dust and fume from the gas, discharging to the atmosphere a portion of the clean heated gas flowing from the precipitators, mechanically recirculating separate streams of a second portion of the clean gas from said precipitators into a common chamber and thence into said hot gas stream, and humidifying the recirculated gas by introducing water thereto and vaporizing the water by sensible heat of the gas.

2. In the operation of a Portland cement plant comprising a plurality of clinkerlng kilns each communicating with its individual electrical precipitator, the method that includes passing a stream of hot gas from each kiln through an electrical precipiator operating to remove dust and fume from the gas, discharging to the atmosphere a portion of the clean gas flowing from the precipitators, mechanically recirculating separate streams of a second portion of the heated clean in a multiple kiln the hot gases from gas from said precipitators into a common chamboiling temperature of water, a pressure equalizer vented to the atmosphere and thence into ing chamber, recirculation ducts leading from said hot gas stream, and humidifying the resaid discharge ducts to said chamber, means circulated gas by introducing water thereto and conducting gas from said chamber into the kiln vaporizing the water by sensible heat of the gas stream in advance of said fans, and means gas. for introducing moisture to and for vaporization said kiln to the precipitator, a fan in said duct, 6. The combination comprising a pair of Portin said circulating duct, and mean for introperature of water, a pressure equalizing chamber ducing Water into the clean gas stream in the vented to the atmosphere recirculation ducts recirculation duct for vaporization by the sensileading from said discharge ducts to said chamble heat of the gas recirculated by said second h r, means onduc in gas fr m s i ch mb fan. into the kiln gas stream in advance of said fans,

4. The combination comprising a Portland fans displacing gas through said recirculation discharge duct leading from the precipitator and HARRY I R. containing gas at a temperature considerably WILLIAM C. CAMPBELL. in excess of the boiling temperature of water, a clean gas recirculation duct leading from said References Cited In the file of thls Patent discharge duct into the outlet end of the kiln, UNITED STATES PATENTS a second fan in said recirculation duct, and Number Name Date means for introducing water into the clean gas 1 185 136 Seaman May 30 1916 stream in the recirculation duct for vaporization 12O4906 Schmidt g Nov 1916 by the sensible heat of the gas recirculated by 1:790:961 Welch d 1931 Sam Second 1,820,726 Bayha et al Aug. 25, 1931 5. The combination comprising a pair of Port- 1,909825 Hahn et aL May 16, 1933 land cement clinkering kilns, an electrical pre- 2,332,253 Penney et aL 14, 1945 FOREIGN PATENTS 40 Number Country Date ing from the precipitators and containing gas 3331043 Great Britain 1930 at a temperature considerably in excess or the 553,176 Germany sept- 1932

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