US2369573A - Process and apparatus for the concentration of sulphuric acid - Google Patents

Description

b. 13, 1.945. M. J. KALo'usv-ETAL 2,369 573 PROCESS AND APPARATUS FOR 'THE CONCENTRATION OF SULPHURIC ACID Filed April 8, 1942 REGENERATOR SUPERHEAYEO IHVEHTOIZ$=.

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Patented Feb. 13, 1945 FFl-CE" PROCESS AND APPARATUS FOR THE CON- CENTRATION OF SULPHURIC ACID Mieczyslaw Joseph Kalous and Niels Edward Rambush, Stockton-on-Tees, England Application April 8, 1942, Serial No. 438,202

In Great Britain April 8, 1941 Claims.

This invention relates to an improved process for concentrating spent or other dilute sulphuric acid by the use of superheated steam.

The objects of the invention are to overcome difllculties met with in providing continuous heat exchangers to superheat steam to temperatures,

of 600 C. and higher and to provide a robust plant construction with a high thermal economy.

Other objects will appear hereinafter.

According to the invention, the material is concentrated by direct contact with steam which has been superheated on the regenerative principle. This has advantages over indirect heating, since we find that the steam should be superheated to above 600 C. to produce sulphuric acid of 95% strength and this would involve the employment of heat resisting steel if a superheater of the indirect type .were used. The invention further includes methods of purging the system and of economising steam as hereafter described.

For concentrations over 95% it will be neces-.

sary to employ more highly superheated steam.

The superheater chambers may be filled with any type of refractory chequer bricks as used in regenerator practice, and arranged to work on a cycle so that the chequer bricks are alternately superheated steam entering the acid concentration plant be maintained substantially constant. This is achieved by the provision of a by-pass connection and valve across the supply of low temperature steam and superheated steam, the valve being automatically controlled to allow the required amount of low temperature steam to mix with the superheated steam.

An example of how the invention may be carried out in practice is given with reference to the accompanying drawingwhich is a diagrammatic arrangement.

l is a concentrator in which sulphuric acid is concentrated by means of superheated steam entering at IS with low temperature steam leaving at l5, land 3 are regenerators provided with burners 4 and 5 respectively, combustion chambers 6 and I respectively, refractory chequer bricks '8 and 9 respectively, supported on refractory supports ,Ill and H respectively. The chequer bricks are suitably stacked and may be of any type as used in regenerator practice.

The burners 4. and 5 are fed withfuel gas or fuel oil from supply line l3 through valves l8 and I9 respectively. The necessary air for combusticn is fed from supply line it through valves 20 heated and then cooled while at the same time superheating the steam. The heating medium may be fuel gas or fuel oil or solid fuel or pulverised'fuel.

During one stage of the cycle one or more regenerators are heated by direct contact with hot products of combustion and during another stage of the cycle steam is passed over the heated I chequer bricks for the purpose the steam. p

In the concentration ofsulphuric acid by means of superheated steam, the steam leaving of superheating plus that corresponding t the Water which is evaporated from the acid being concentrated.

In a preferred form of the invention, low temperature steam leaving the acid concentrator is superheated in the manner described, no external supply of steam being used except for make-up purposes. The excess steam corresponding to the amount of water which is evaporated in the concentrator is used for purging the regenerators and 2| respectively.

Instead of fuel gas or fuel oil or pulverized fuel solid fuel can be used in which case the burners 4 and 5 are replaced by furnaces in which the fuel is burned with air.

Hot products of combustion pass up through combustion chambers 6 and l respectively, down through chequer bricks 8 and 9 respectively and out through valves 22 and 23 respectively to stack l2. Heat is abstracted from the-hot gases and stored in the chequer bricks.

- the acid concentrator consists of an amount equal to the initial quantity of superheated steam During another stage of the cycle, low temperature steam leaving the concentrator I at l5 enters the bottom of the regenerators through valves 24 and 25 respectively, passes up through the chequer bricks and down the combustion of products'of combustion, the heat stored in the other regenerator is utilised in superheating steam.

.It is desirable that the temperature of the Before changing over a regeneratorv from in regenerator 3.

heating to steaming" it is desirable to purge the regenerator free from products of combustion. This is to ensure that the superheated steam leaving the regenerator is as far as possible free from permanent gases. The steam for purging the regenerators is fed from supply line H through valves 28 and 29 respectively and passes out through valves 22 and 23 respectively to stack I2.

In the process of sulphuric acid concentration it is necessary to bleed 01f that amount of steam corresponding to the water which is evaporated from the sulphuric acid bein concentrated. According to a preferred .form of the present invention the steam which is bled off from the sulphuric acid concentration plant is passed to supply line H and utilized for purging the regenerators.

The temperature of the superheated steam leaving a regenerator will be higher at the beginning of the steaming period than at the end of the steaming period. It is desirable to maintain the temperature of the superheated steam entering the concentrator I at I6 substantially constant. This is achieved by providing a bypass connection and valve 30'across the supply of low temperature steam leaving the concentrator at 15 and the supply of superheated steam entering the concentrator at I6. The valve 30 is automatically controlled by the controller 3| so. as to maintain the temperature of the superheated steam entering the concentrator at I6 substantially constant. 4

At a certain stage of the cycle of operation, regenerator 2 will be on heating and regenerator 3 on steaming. Valves I9, 2|, 23, 24, 26, 28 and 29 will be closed and valves I8, 20, 22, 25 and 21 open. Fuel and air burn in burner 4 and the hot products of combustion pass up through combustion chamber 6, down through the chequer bricks 8 and out through valve 22 to stack I2. Low temperature steam leaving the concentrator I at I passes through valve 25 at the bottom of regenerator 3, up through chequer bricks 9 and down combustion chamber 1, leaving the regenerator through valve 21 in a superheated condition. This superheated steam enters concentrator I at I6, the temperature being maintained substantially constant by allowing the admixture of some low temperature steam through thermostatically controlled valve 30.

After a given time, when the necessary amount of heat has been stored in the chequer bricks 8, valves I8 and 20 are closed and the burner 4 put out of operation. Valve 28 is then opened and steam passed to the regenerator 2 from supply line H. This steam passes up combustionchamber 5, downthrough chequer bricks 8 and out through valve 22 to stack I2, purgin regenerator 2 free from products of combustion.

After purging regenerator 2 with steam from supply line I1, valves 24 and 26 are opened and valves 22 and 2,8 closed. Simultaneously, valves I9, 2I and 23 are opened and valves 25 and 21 closed. The low temperature steam leaving concentrator I at I5 now passes through regenerator 2, in which it becomes superheated, while fuel and air burn in burner 5 and the hot prodchequer bricks 9 and out through valve 23 to stack I2, purging regenerator 3 free from products of combustion. I

After purging regenerator 3 with steam from supply line H, valves 25 and 21 are opened and valves 23 and 2,9 closed. Simultaneously valves I8, 20 and 22 are opened and valves 24 and 26 closed. The cycle is then recommenced with regenerator 2 on heating and regenerator 3 on steaming.

The valves may be operated by hand or they may be automatically controlled according to a set cycle.

The invention is not limited to the use of two regenerators. Several regenerators may be taken and the cycle of operation so stepped that one or more of the regenerators are on steaming while the other regenerators are either on heating or being purged.

The invention is further not limited to the use of low temperature steam from the acid concentration plant. An external supply of steammay be used, superheated in the manner described and the superheatedsteam passed to the acid concentration plant.

We declare that what we claim is:

1. A cyclical process of concentrating sulphuric acid in which a body of heating steam is maintained in continuous flow in a closed circuit and comprising alternately heating up two beds of refractory material by burnin fuel in contact therewith, superheating steam to above 600 C.

\ to be re-superheated thereby, bleeding off another portion of said low-temperature steam-and passing the same in contact with the said other bed thereby to purge said other bed of combustion gases, and then diverting the flow of said main portion of steam to said other bed while heating the said one bed by burning fuel in contact therewith.

2. A cyclical process of concentrating sulphuric acid in which a body of heating steam is maintained in continuous flow in a closed circuit and comprising alternately heating up two beds of refractory material by burning fuel in contact therewith, superheating steam to above 600 C in one of said beds while the other is being heat ed up, continuously passing said superheated steam in substantial absence of foreign gas in contact with sulphuric acid and thereby concentrating said acid and producing low-temperature steam containing additional steam evaporated from said acid, passing a main portion of said low-temperature steam in contact with said one bed to bare-superheated thereby, bleedin ofl another portion or said low-temperature steam ucts of'combustion heat upthe chequer bricks 9 When the necessary amount of heat has been stored in the chequer bricks 9, valves I9 and .2I are'closed and the burner 5 put out of operation. Valve 29 is then opened and steam passed to reenerator 3 from supply line I1. This steam passes up combustion chamber I, down through in amount substantially corresponding to the water which is evaporated from said acid and passing at least a part of the bled-off steam in contact with the said other bed thereby to purge said other bed of combustion gases, and then diverting the flow of said main portion of steam to said other bed while heating the said one bed by burning fuel in contact therewith.

ing low-temperature steam in contact with said bed thereby to purge the same of combustion gases, thereafter passing low-temperature steam in contact with said bed vand thereby superheating the steam to above 600 C., passing said superheated steam in substantial absence of foreign gases in contact with sulphuric acid and thereby concentrating said acid and producing low-temperature steam containing additional steam evaporated from said acid, passing a main portion of said latter low-temperature steam into.

contact with said bed to .re-superheat the same and then passing the same for contact again with sulphuric acid, and bleeding off that amount of steam prior to said latter contact with said bed which corresponds to the water which is evaporated from said acid.

4. A cyclical process of concentrating sulphuric acid, comprising heating 1a bed of refractory material by burning fuel in contact therewith,

passing low-temperature steam in contact with said bed thereby to purge the same of combustion gases, thereafter passing low-temperature steam in contact with said bed and thereby superheating the steam to above 600 C., passing saidsulphuric acid, and mixing another portion f the low-temperature steam with the superheated steam in a ratio dependent upon the temperature of the superheated steam as it comes from the bed whereby to maintain constant the temperature of the steam contacting the sul ohuric acid. a

5. A cyclical process of concentrating sulphuric acid, comprising heating a bed of refractory material by burning fuel in contact therewith, passing low-temperature steam in contact with said bed thereby to purgethe same of combustion gases, thereafter passing low-temperature steam in contact with said bed and thereby superheating the steam to above 600 C., passing said superheated steam in substantial absence of foreign gases in 'contact with sulphuric acid and thereby concentrating said acid and producing low-temperature steam containing additionalsteam evaporated from said acid, passing a main portion of said latterlow-temperature steam into contact with said bed to re-superheat the same and then passing the same for contact again with sulphuric acid, and bleeding off another portion of said latter low-temperature steam and passing the same through a second directly-heated bed to purge combustion gases therefrom preliminary to employment of said second bed for superheating steam for concentrating sulphuric acid.

MIECZYSLAW JOSEPH KALOUS. NIELS EDWARD RAMBUSH.

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