US2386292A - Dehumidification method and means - Google Patents

Description

DEHUMIDIFICATION METHODS AND MEANS ATTORNEY.

Get. 9, 1945. WQ H. CARRIER DEHUMIDIFICATION METHODS AND MEANS Filed April l0, 1941 5 Sheets-Sheet 2 a Bevis 'n asvls INVENTGR.

WILLIS H. CARRIER ATTORNEY.

ct. 9, 1945. W H CARRlER 2,386,292

DEHUMIDIFICATION METHODS AND MEANS Filed April l0, 1941 l 3 Sheets-Sheet 3 FIG. 3

mvENToR. WILLIS H. CARRIER BY 4 /m ATTORNEY.

Patented @ctr k9, i945 Willis H.- Carrier, Syracuse, N. Y., assigner` to Syracuse, N. Y., a corpo- Carrier Corporation, ration of Delaware Application April 10, i941, Serial No. 3B7,948

4 Claims.

This invention relates to methods of and apparatus for conditioning air employed in the operation of blast furnaces.

In the smelting of ores, great quantities of air are necessarily employed. 1t is known that excessive moisture content of the air, as is prevalent under summer operating conditions, may at times reduce the capacity of a blast furnace as much as This is due to thefact that a blast furnace may be considered to be a gas producer, and as such it dissociates moisture introduced by the blast. This requires a considerable expenditure of energy supplied by the fuel and consequently leaves that much less fuel available for the smelting process. It should be noted that thisl expenditure of fuel is not utilized to any degree in removing or dissociating moisture contained in the coke or ore since such moisture is' evaporated by the drying action of the blast furnace gases, after such gases leave the active smelting zone. Hence the use of fuel required for dissociatng moisture is confined solely to the air used in the blast.

A principal object of the invention is to control the moisture content of the air employed in blast furnaces, whereby the air introduced will have substantially a constant absolute humidity,

denitely established preferably at a. point between 21/2 and 3 grains per cubic foot of air. Since the air, under summer operating conditions, in most parts of the United States, often has an absolute humidity twoor three times as great or even more, the result is that the introduction into the furnace of air with so small an amount of absolute moisture, may often effect an annual increase in capacity of a given furnace on the order of 7-10% without any increase in coke consumption, While this saving may be attribof the blast.

Another object of the invention is to enable' While a considerable amount of power is necessary to drive the refrigerating machines provided for effecting required dehumidication of the air, the power required for driving the fans or blowers serving the furnaces is reduced due to the reduction in weight of the air resulting from the precipitation of moisture therefrom', and applicant has found that no appreciableincrease of power `is required for driving both the blowers and the refrigerating machines over that required for operating the blowers alone when the airs moisture content is not removed.

lAnother object of the invention is to control the absolute-humidity of air introduced into a blast furnace so that the furnace temperature may not be aiected due to change in moisture burden. The quality of smelted iron, particularly with respect to silicon content, depends in great measure on the furnace temperature. While the temperature is aiected by changes in burden, it ls also affected by variations in moisture content of the blast, so that the production of iron meeting exact standards of composition has not only been made dimcult but costly without a means, such as that provided by applicant, for regulating the moisture content of the blast.

centrifugal fans or blowing engines to operate with stabilized displacement and at consequent stabilized speeds. By providing air substantially uted to the elimination of the necessity for using up coke for dissociating moisture in the blast,

another feature, of utmost importance, owing from the use of air at a xed moisture content, isv that operations may always be carried forward on a `xed schedule as to time and loading, free of variations heretofore made necessary because` of varying weather. conditions resulting in air having widely diierent absolute humidities. Thus, the furnace need not be loaded with an excessive quantity of coke to take care of unforeseen burdensar'ising from high absolute humldities and as a result the utmost in ore loading is made possible. Also, the schedule of operations may attain a high degree of regularity with consequent greater capacity since the utmost in smeltlng is achieved in a minimum of time, and

at a constant temperature and with a constant moisture content, the weight of air supplied to the inlet sides of the fans or blowing engines remains substantially the same. lApplicant provides a simple means for controlling and metering the weight of air at all times.

Applicants'system for controlling the air fed tothe blast may readily be combined with existing furnaces' and air blowing engines, so that the benefits of greater furnace capacity, better quality-iron, and more emcient and simplied operation may be attained in a, very short time and at relatively small cost compared to that required, for example, for providing additional smelting capacity.

To achieve these and other benefits, applicant provides a combination of apparatus incorporating the following principal features: (a) a spray type dehumidier in which fogging is substantially eliminated, and anactual dewpoint attained within -a few degrees oi the refrigerant temperature (-b) a multi-stage pumping system temresponsive tc changes in temperature of the water leaving the refrigerating machine en route to the dehumidifier. By correlation of these elements, la constant minimum dewpoint may be maintained with great accuracy, and maximum simplicity, economy and reliability. Of primary importancais that in this system moisture variation due to varying entrainment is eliminated; and the control is largely self-regulatory.

Considering the drawings:

Fig. 1 is intended diagrammaticaily to illustrate the essential elements of a dry-blast system or blast furnace arrangement equipped with a source oi' supply of air adapted to be furnished at a desired rate and containing a constant and predetermined amount of moisture per unit of volume, normally about 2.85 grains per cubic foot of air;

Fig, 2 illustrates diagrammatically an air conditioning system capable of supplying air in de-g sired volume and at a desired condition, for use in the blast furnace and;

Fig. 3 illustrates diagrammatically a section of the washer employed in the system of Fig. 2.

First considering the smelting process, and as is well known to those skilled in the art, the furnace 4 is charged at the top in the usual manner with the burden consisting of ore, coke, fluxes, etc. The wind or blast enters the furnace through the tuyres 5 immediately above the hearth. In prior practice it was customary to load an excess of coke with respect to the tonnage of ore to compensate for a possible rise in moisture'content in the air of the blast. Otherwise, it was' necessary to vary the temperature of the hot blast fed to the furnace, and in this connection it is necessary to provide an additional 25 to 50 for each grain of moisture per cubic foot of air. pacity in the stoves 6 where the air, in the usual manner, is preheated to a temperature above 1000 before being delivered to the furnace. If

- no such reserve capacity is available, or if no excess of coke in the furnace is available, there is danger of the furnace growing cold, with attendant serious loss in production, and expense. This becomes apparent when it is realized that the heat-*absorbed by one pound of moisture vapor to produce its dissociation amounts to- 2850 B. t. u. and this requires added fuel. Since the quantities involved are enormous, with the' wind required for a furnace of about 500 tons capacity per day amounting to about 50,000 cubic feet of air per minute (or 2700 tons of air per day, which means over 5 tons ofA air per ton of iron` produced) it will be seen that the savings iiowing from reduction of moisture content of the air are very appreciable. Each grain saved Der cubic foot per minute amounts to more than 5 net tons of water per day. Since it is not uncmmon on humid summer days to have nine or more grains per cubic foot, the elimination of six grains per cubic foot, results in preventing over 30 tons of water from entering each furnace.

Thus, applicant provides a system of air moisture control, generally designated by numeral 1 f for regulating the moisture content of air delivered to the blowing engines or the like 8, from which the air enters the stoves and then the furnace in the usual manner. The consequence of providing system 1 is to enable at all times the y charging of an exact tonnage of ore and coke,

without regard to unforeseen changes in Weather conditions, so that the blast of air at an assured and constant condition will cause the production of a constant quantity of iron per unit of time. Since the charge must be introduced some l0 to 12 hours before it reaches the hearth, it is evident that with all factors predetermined, operations may proceed at maximum emciency with the furnace at full productive capacity. For

\ every grain of moisture removed per cubic foot of iron are saved. Thus not air, a saving of about 48-50 pounds of coke per ton of iron is effected. For every six grains removed, as is the case under summer operating conditions,

only can the furnace be operated with assured regularity, but more ore may be safely charged and more iron produced with less coke. Actual operations with applicants system over extended test periods, with charges employing varying grades of ores, shows an increase in iron production of approximately 10% with a decrease in consumption of coke of ap proximately 10%.

Considering the system for producing the dry blast, as illustrated in Fig. 2, numeral I0 designates a centrifugal refrigerating compressor adapted to be driven .by steam turbine II, to which steam is supplied at a desired pressure from any available source I4. Cooler I2 is operatively associated with compressor I0, and although it is diagrammatically illustrated as a separate piece of apparatus, it is usually combined in a unitary assembly with the compressor, and this is often also the case with refrigerant condenser' I3. Steam condenser I5 serves turbine II. A common water supply from source I-G is routed by motor driven pump I1 through condensers I3 and I5 in series, and then delivered through discharge line I8 to a cooling tower for reuse in the system, or wasted.

The refrigerant circuit is from compressor I0 to condenser I3 through discharge line 22 where the refrigerant is liquefied in the usual manner; then from condenser I3 through trap I9 and supp ly line 20 to cooler I2 where it is evaporated; and then in gaseous state from cooler I2'back to the compressor through suction line 2|.

The water circuit is as follows: from sump 23 of the first stageof dehumidification apparatus tanks under the respective dehumidifier stages.L

The pumps 25 and 30 are designed to deliver the water handled by them to the respective sprays served by them at 25 pounds pressure.

The air iiow through apparatus 1 in countercurrent relationship with reference to the direction of discharge of the water from sprays 28, 29, 33 and 30.` The proportions of weight of air routed through apparatus 1 with respect to the weight of water delivered throughrthe sprays is such that substantially of the required cooling effect of the air is accomplished the first stage of apparatus 1. To obtain this result applicant supplies approximately .'7 pound of water about 300 pounds of coke per ton of asaaaaa approximately 1.4 pounds of water per pound of air in each stage.

This relationship produces an overall rise in water temperature of approximately when a corresponding amount of air is cooled through a Vrange of 40 in wet bulb temperature, for example, from 80 to 40. The ratio of .7 pound of water per pound of air in each bank of sprays l may be varied, within limits, yet permit achiev- Where a surgel in flow is encountered, as when reciprocating blowing engines are employed, the maximum practical velocity is less than that which may safely be employed when continuous air ow is provided as where turbo compressors are used for providing the blast. Such operation will prevent entrained moisture from being carried through the eliminators.

Control 2l is specially adapted to provide waterv at a desired temperature to apparatus l to assure delivery therefrom lof air leaving the second stage at a predetermined dewpoint. In oonnection with control 2l, the operation oi centrifugal compressor i0 is signicant. Compressor i0, in practice, produces a diderence in temperature between evaporator and condenser, depending upon the speed of operation of the .compressor. Considerable changes in capacity of the compressor can occur at a given temperature difference without greatly affecting the speed of Vthe compressor. However, the rate of flow of heat in the water cooler I2, as well as in condenser i3, depends` upon the difference in temperature between the water and the refrigerant on opposite sides of the finned heat transfer surfaces prod@ vided therein. Thus, it is possible to change the load on the compressor as well as the temperature, merely by changing the speed of the compressor, which may be brought about by regulating the operation of turbine i i.

In the instant application, the aforesaid characteristic of the centrifugal compressor may be utilized to control the temperature oi' the water delivered to the sprays by means ci' Va very simple speed control of the compressor, actuated by the temperature of the water leaving cooler i2.

In practice, control 2l governs the speed of tur-1 bine il by regulating the admission of steam thereto from source Iii. Since the turbine iscoupled to the compressor, this control effectively governs the speed of the compressor. However, since the total load, as it varies, aiects the dewpoint oi' theair delivered from apparatus l, and since it is desired to keep the variation'within exceedingly small limits it is necessary to reset control 2l as the total load varies. The change in total load may be measured by the change in temperature of the water from sump turned to the cooler. the change in total load on the system, serves to reset control 21 whereby the speed of the cornpressor will be varied and the temperature of water delivered correspondingly varied to compensate for changes in total load. As a result, the dewpoint of the outgoing air may be maintained substantially constant.A

To illustrate the operation oi' the control, -it may be assumed that the spread between the temperature of the air leaving the second stage and the temperature of the water from the cooler 23 being re- Thermostat 35, reflecting delivered to thefsecond stage is 2, which is the actual condition as it exists at mammum load. Under practical operating conditions the water temperature entering the second stage may be 38 for a 40 dewpoint of the leavingair at maximum load. The water-returning from the first stage to the cooler is 48 or 10 higher than the water leaving the cooler. At half load. however, the f rise in water temperature is 5"y and.v the spread between the leaving air and the entering water is only l". Therefore, for a 40 dewpoint of leaving air, the water temperature leaving the cooler and entering the second stage, under half load conditions, would be 39 and the water temperature leaving the rst stage and entering the cooler would be 44. Therefore, thermostat 35 causes control 21 to be raised or reset 1 for every 4 rise in entering water temperature where the total rise in water temperature at full load is 10.

Obviously, the resetting of control 2l, which may be accomplished manually as well as automatically, is regulated so that the degree of reset is proportionate to the change in water temperature entering the cooler. Thus; if the rise in water temperature is 12 instead of 10 at full load, then the control would be reset 1 Vfor every 5 rise in the temperature of the water leaving the dehumidifier apparatus l and entering the cooler it.

By means of this system oi' control of the ltemperature oi the leaving water, utilizing a reset operated by or in accordance with variations in the temperature of the water entering the cooler, it is possible precisely to control the dewpoint of the air leaving apparatus and this may be done by controls located at the refrigerating machine, although this is often installed in a separate building removed from the apparatus l.

Fig. 3 illustrates in greater detail the dehumidifier arrangement employed. The air to be conditioned is preferably drawn in from outdoors through a vertically disposed inlet tt. The intake chamber may be provided with an air distributor tlconsisting of a series of blades for causing the air to flow uniformly in a horizontal direction into the first spray chamber or first stage of the dehumidiiled apparatus. As was already noted, the iirst stage of air cooling constitutes the second water pumping stage; and the second stage of air cooling constitutes the first wafer pumping stage. Each spray chamber or stage is provided with two banks of sprays. These sprays are of the centrifugal type in which the water is discharged in opposition to the direction of air iiow. To prevent the spray carrying within tbe. air inlet 3d a series of bao plates orv eliminators 3a are positioned at the entrance to the rst spray chamber. These are vertical plates so designed and arranged as to effect a uniform lateral distribution of the air throughout the chamber. These plates serve a special purpose in uniformly distributing the air in order more effectively to obtain a uniform dewpoint temperature and prevent"fogging of the air passing through the chamber. i

Stages one and two in effect constitute two compartments. A single vwater tank is provided below the two compartments but this contains a vertical partition 39 which divides thetank into two parts. An equalizer opening E0 in partition 39 permits water to flow from one of the tank coirnpartments to the other whenever there is a 1 of the air.

through opening pumping system or overflow of one of the tanks which might otherwise occur.

At the discharge end of the iirst spray cham- .ber or first stage is positioned a three-bend eliminator Il and at the entrance to stage 2 is positioned a series of bailies 42. Eliminators 4l effectively remove entrained moisture from air leaving stage l this moisture draining into sump 23. Battles 42 prevent spray from carrying through beyond stage 2, the water from these bafiles dripping into sump 3l. Bafiles l2 are also 40 and prevents failure of theI designed to distribute uniformly the air entering stage 2, and this is of importance in securing a uniform dewpoint and in preventing fogging" positioned a six-bend eliminator 43 which effectively prevents any entrained moisture from being carried from the second stage into the exit or plenum chamber 4l. The air from the plenum chamber goes through discharge conduit :i5 to the blowing engines 8, and from there to stoves 6 and blast furnace 4, as is well known in the art.

Instead of providing a thermostatic device for resetting control 21, a recorder may be employed l for noting the dewpoint of the air delivered from the second stage. When an undesirable varia.- tion occurs an operator may then manually reset control 21. The control, which reects the temperature of the water delivered from the cooler I2 will then, responsive to its new setting, cause the turbine to increase or reduce the speed of the compressor until the water temperature from the cooler satisiied the new setting.

With applicants method of control overspeeding of the compressor and undercooling of the spray water which might result in a freezing dondition within tlfe cooler is prevented.` since the water temperature is controlled without any cycling or surging of temperatures, either of the Vwater or of the dewpoint of the leaving air.

- Since the invention exemplifiedby the system disclosed may be practiced with modifications in design of apparatus as well as in the method of operation employed, obvious variations are intended to be covered, and the terms ofthe appended claims .are not intended to be limited to the specific combination and steps employed.

I claim:

l. A method of treating air for use in a blast furnace wherein the condition of the air delivered to the furnace is regulated consisting inv cooling the air from its entering condition to a predetermined iinal condition where it contains substantially 3 grains of moisture per cubic foot of air, accomplishing a preponderant percentage of desired cooling of the air in a first air treating stage, spraying water in said first stage, propor` tioning in said first stage the weight of air andv weight of water spray to produce said preponderant percentage of desired air cooling, accomplishing said la'st mentioned step by spraying between one-half pound and one pound'of water per bank of sprays per pound of air passing through said ilrst stage, utilizing at least two banks of spray in said first stage and accomplishing the balfancepf desiredair cooling by passing the air from the sprays of the first stage to other sprays in a second stage.

2. A method of treating air for use'in a blast furnace wherein the condition of the air delivered to the furnace is regulated consisting in cooling the air from its entering condition to a predeter- At the discharge end of stage 2 isV Aso chine,

mined iinal condition a-t substantially 40" F., passing the air to be conditioned through a plurality of stages of conditioning arranged in series, each ofwhich provides two banks of spray and substantially complete elimination of entrained moisture fromthe air as the air leaves each stage, providing a rise in the temperature kof the water for the sprays after it passes through all stages of approximately 10 perature yof the air after it passes through all stages of approximately 40 F., said water iiowing from the iinal stage to the first stage in counteriiow relationship to .the passage of the air through the stages accomplishing substantially 80% of said rise in water vtemperature and drop in air temperature in the first of the stages of conditioning by supplying approximately .'I pounds of water in each of the banks of spray per pound of air passing through the sprays, routing the air through the sprays at, a velocity between 400 and 600 feet per minute. and regulating the temperature of the water serving the sprays to maintain a definite number of grains per cubic foot of air leaving the final conditioning.

3. A method of treating air for use in a blast furnace wherein the condition of the air delivered to the furnace is regulated consisting in cooling the air from its entering condition to a predetermined final condition Vin a plurality of stages, accomplishing approximately 80 per cent of desired conditioning of the air in a. first air treating stage, accomplishing the balance of desired conditioning of the air in a remaining air treating stageeliminating entrained moisture at the discharge side of each stage and preventing fogging of air passing through the stages. cooling water for delivery to said last mentioned stage and thereafter to said nrst air treating stage,

14o measuring the dewpoint ofthe air subsequent to treatment in said last stage, and controlling the temperature of the water fed to said stages responsive to variations in temperature of the water leaving the first stage whereby the air delivered from said last stage tained substantially constant.

4. A system for treating air for use in a blast furnace consisting of a first conditionin'gpfchamber, a second conditioning chamber, a plurality of sprays within each of said chambers, means located at the discharge ends of. each chamber for eliminating entrained moisture from air leaving each chamber, a. centrifugal refrigeration mameans for driving said machine at varying speeds, a cooler served by said machine, means for is lmainrouting water from the cooler to the second chamminute, regulating the temperature of the water delivered from the cooler by means located in a line discharging from .the cooler end in a second line leading to the.cooler, said second means regulating the action of the first means.

WILLIS H. CARRIER.

F. for a drop in the iemstage of the dewpoint of

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