US1964594A - Method of cleaning mercury boilers - Google Patents

Description

252. COMPOSITIONS, UrOss iiBTGlGflCB 7 Exam,

June 26, 1934. A, J. NERAD El AL 1,964,594

METHOD OF CLEANING MERCURY BOILERS Filed Jan. 2s, 19::

Inventors:

Anthony. J' Nerad, Burt L.Newkir"k,

Their Attorney.

Patented June 26, 1934 UNITED STATES METHOD OF CLEANING MERCURY BOILERS Anthony J.

Nerad and Burt L. Newkirk,

Schenectady, N. Y., assignors to General Electrio Company, a corporation of New York Application January 26, 1933, Serial No. 653,650

12 Claims.

The present invention relates to methods .of cleaning mercury boilers or mercury vapor generators.

The capacity of a mercury boiler depends upon the heat transfer of the walls of the boiler. This heat transfer is affected by the degree of wetting of the boiler walls by the mercury. A mercury vapor generator in which the mercury does not wet the boiler wall has a much lower capacity than one in which the mercury liquid wets the walls. To secure such wetting it is advantageous to clean those heat transfer surfaces of the boiler which are in contact with the mercury to remove scale, slushing compound, or other foreign materials so that the clean steel walls of the heat transfer surfaces may be brought into intimate contact with the mercury. Since the erection of 'a mercury boiler with its associated apparatus requires a period of months during which oxidation or other impairment of cleaned steel surfaces may occur before the mercury is put into the boiler it is advantageous to use a cleaning process that can be applied after the boiler has been erected and is otherwise ready to run.

Furthermore, in the operation of mercury boilers it has been found that deposits of iron, iron oxide and other substances are formed in the interior of the boiler. These deposits decrease the heat transfer to the boiler and have other serious consequences, interfering with the operation of certain parts of the boiler. This renders periodic removal of deposits necessary.

One object of the present invention is to provide an improved method of cleaning mercury boilers either before and after they have been in operation whereby mill scale or other impurities or foreign substances as well as deposit formed during operation of the boiler may be removed from the heat transfer surfaces after the boilers have been erected and/ or operated in the field.

For a consideration of what we consider to be novel and our invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawing in which we have shown a typical construction of a present-day mercury vapor power plant provided with certain elements for permitting the cleaning of the boiler in accordance with our invention.

The plant shown in the drawing comprises a furnace having a wall 10. Arranged within the furnace are a plurality of drums ll, 12 containing mercury liquid to be heated and evaporated. Connected to the lower portion of each drum are a plurality of liquid circulating and evaporating tubes 13, each of which comprises an outer tube 14 fastened to the wall 15 of the drum and an inner tube or core 16 projecting into the drum and fastened to a baffle plate 18 arranged within the drum. The inner tube has a passage 19 receiving liquid from the space above the baflie plate. The lower end of passage 19 communicates with a space 20, hereafter termed vapor space, defined between the inner and the outer tubes. During operation, the liquid flows through the liquid passage or space of the inner tube into the vapor space where it is partly evaporated and returned to the drum. A displacer block 21 is arranged within each of the drums for displacing a portion of the liquid to permit operating the plant with a smaller amount of mercury liquid. The drums are connected to each other by liquid equalizing pipes 22 which preferably are arranged above the cold liquid level in the drums, as disclosed in, the copending application of B. P. Coulson, Jr., filed December 29, 1932, Serial No. 649,350. In the present example we have shown another liquid heating and evaporating element 23, having a header 24 communicating with the drum or drums through a conduit 25. The heating element 23 comprises down-tubes 26 connecting the upper header 24 and a lower header 2'7, and up-tubes 28 arranged inside the furnace wall and connecting the lower header 2'? with the upper header 24. During operation, liquid is conducted from the drum or drums to the upper header 24, whence it flows through the down-tubes 26 to the lower header 2'1 and thence into the up-tubes 28 in which it is at least partly evaporated. The liquid expelled from the up-tubes 28 into the upper header 24 is recirculated and the vapor is conducted to the drum or drums. The drums are connected by conduits 29 and 30 respectively to a vapor supply conduit 31. The latter conducts the vapor produced in the drums to a consumer, in the present instance shown as an elastic fluid turbine 32 having a valve 33 for regulating the'admission of elastic fluid to the turbine. The exhaust fluid of the turbine is condensed in a condenser 34 having cooling means 35. The condensate is returned to the drum through a conduit 36 having branches 3'! and 38 connected to the drums l1 and 12 respectively. Conduit 36, which may be termed a liquid supply conduit, is preferably located above the cold liquid level in the drums as disclosed by the aforementioned application of Coulson.

Our method for cleaning a mercury boiler comprises a plurality of steps to be applied in their proper sequence. These steps apply both to 252. COMPOSITIONS,

' a moderate temperature.

.the boiler. with our invention by flushing the boiler with water. In the drawing we have shown two valves,

boilers to be put into operation and boilers which have been in operation, with the exception of the first step, namely, the removing of the mercury from the boiler, which obviously applies to boilers only which have been in operation.

A mercury boiler of the type described comprises a number of parts, such as the heating units 23, and particularly the heating tubes 13 which define spaces or dead ends from which the mercury cannot be drained through valves. In cleaning a boiler which has been in operation we remove the mercury liquid by evaporation. The vapor thus formed is condensed and stored in the turbine condenser or like containers. As the turbine condenser may be too small to contain all the mercury of the boiler, we may provide auxiliary containers. In the present instance we have shown a container 39 having an inlet conduit 40 provided with a valve 41 and connected to the vapor conduit 31. An outlet conduit 43 for the container 39 including a valve 44 is connected to the liquid header 36. The container 39 is provided with cooling means 45 for condensing the vapor conducted to the container. During the removing of the mercury we maintain preferably a slow fire in the furnace to prevent overheating of certain parts of the boiler. Maintenance of a good vacuum in the boiler during this step permits evaporation of the mercury at The valves 33 and 41 are opened whereas valves-44 and a valve 49 in conduit 36 are closed so that the vapor rising from the boiler is conducted through the turbine to the condenser 34 and through conduit 40 to the auxiliary container 39. After the entire liquid is thus removed from the boiler, valves 41 and 33 are closed.

After the liquid has been removed from the boiler we fill the boiler with a cleaning or pickling solution adapted to remove impurities or deposits from the boiler walls. We have found that an acid solution, preferably a diluted solution of hydro-chloric acid attacks vigorously the scale, and other deposits on the interior of the boiler walls. The solution disintegrates, dissolves, undermines, and broadly speaking, removes the deposits within a comparatively short time. Tests have shown that the application of a diluted solution of hydrochloric acid for about two hours to the boiler walls is sufiicient to remove the deposits therefrom. The deposits are partly dissolved by the acid solution, forming compounds therewith, and partly maintained in suspension in the solution. In the choice of the cleaning solution to be employed and the strength of the .solution, care must be taken to adjust the factors of time, temperature and strength of solution.

If the parts of a new boiler have all been cleaned thoroughly in the process of manufacture and .covered for protection with a greasy, slushing compound, such compound may be removed by a non-acid solvent cleaning solution.

The next step of our cleaning method comprises the removing of the cleaning solution from This is accomplished in accordance one valve 46 in the vapor conducting conduit 31, and another valve 47 forming a part of a conduit 48 connected to the liquid equalizing pipe 22 between the drums. For removing the cleaning solution from the boiler, valves 46 and 4'7 are opened and water is supplied through conduit 31 to the drums and drained therefrom through the Cross .ieierence equalizing pipe 22 and the conduit 48 connected thereto. While water is thus circulated through the drums and maintained at a level near the normal liquid level in the drum, we maintain a slow fire in the boiler to cause circulation and agitation of the cleaning liquid contained in the heating tubes and the heating units in order to cause mixing of the cleaning liquid with the water and to maintain small solid particles removed from the boiler walls and not dissolved by the cleaning solution in suspension. With the circulation of water through the drums and the circulation of the liquid contained in the heating tubes and units the solution becomes more and more diluted. This process is continued until the liquid is free from cleaning solution. This can be easily tested by well known methods, for instance, by means of blue litmus paper which turns red as long as liquid drained from conduit 48 contains acid.

The next step of our cleaning method is to remove the water from the boiler drums and replace it by mercury liquid. During this process care has to be taken that no air comes into contact with the interior of the boiler which would cause oxidation of the walls. In accordance with our invention the water contained in the boiler is directly displaced by mercury liquid. The direct displacing protects the boilersurfaces from air because the mercury liquid immediately contacts said surfaces as the water is separated therefrom. With the arrangement shown in the drawing this is accomplished by the opening of valve 44 in conduit 43 and the valve 49 in conduit 36. The mercury liquid contained in condenser 34 and auxiliary container 39 thus flows through conduit 36 and its branches 37 and 38 into the drums 11 and 12. The mercury liquid fiows first into the boiler tubes 13 and displaces the water contained therein and as soon as the mercury liquid reaches the lower level of conduit 25 it fiows into the heating unit 23 and displaces the water therein, the water being drained through the conduit 48. In view of the fact that conduit 22 is preferably arranged somewhat above the cold liquid level in the drum and as water particles still cling to the interior wall of the drum, it is not possible to remove all the water by displacing it with mercury liquid.

The entire removal of the remaining portions of water forms the last step of our invention which comprises the slow heating or drying of the boiler, preferably to a temperature between the boiling temperature of water and that of mercury liquid. During the slow heating the water evaporates and the steam may be drained through the left-hand end of conduit 31 which in a step heretofore mentioned served to conduct the flushing water to the boiler.

According to a modification of the step just described we add an alkaline substance, for example ammonia, to the water used to flush out the acid. This is to prevent oxidation of the steel surface between the pickling operation and subsequent operation of the boiler for generation of mercury vapor.

In accordance with a further modification of our invention we add to the cleaning or pickling solution a pic kl inginhibitor which may be an organic substance such as g lue size or bran to slow down the action of'the clearmfickling solution on the steel without affecting the action of the cleaning solution on the deposits.

With our invention we have accomplished an improved method for cleaning the boilers in Examine? mercury vapor power plants. Practice has shown that these boilers should be cleaned before they are put in operation, as well as periodically during their operation. Summarizing, our cleaning method comprises the following steps:

1. Removing the mercury liquid by slow evaporation, preferably at low pressure (vacuum) in case the method is applied to a boiler which has been in operation;

2. Filling the boiler with a cleaning solution;

3. Passing into and through the boiler (11111118 large quantities of water to flush out most of the cleaning solution;

4. Heating preferably at moderate vacuum the boiler tubes and heating units to cause circulation and agitation to remove the remainder of the cleaning solution and the deposits from the dead ends of said parts;

5. Directly displacing the water with mercury liquid; and

6. Drying the boiler at a temperature intermediate the boiling points of water and mercury to remove the remaining portion of water.

Having described the method according to our invention, together with the apparatus for carrying out the method, we wish to have it understood that changes may be made in both the apparatus and the method without departing from the spirit of our invention and the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of cleaning a mercury boiler which comprises removing the mercury liquid contained in the boiler by heating the boiler, placing a dilute solution of an acid into the boiler, and then replacing the acid solution by liquid mercury.

2. The method of cleaning a mercury boiler which comprises slowly heating the boiler to evaporate and remove the mercury liquid contained therein, placing a dilute solution of an acid for a definite time in the interior of the boiler, and flushing the boiler with water.

3. The method of cleaning a mercury boiler which comprises placing a diluted solution of an acid in the boiler to subject the boiler walls for a certain period of time to the action of the acid whereby deposits on the walls are removed therefrom, flushing the boiler with water to remove the acid and simultaneously heating the boiler to cause circulation and agitation whereby the water and the diluted solution are mixed and particles removed from the boiler walls maintained suspended in the liquid, and then replacing the water with mercury liquid.

4. The method of cleaning a mercury boiler which comprises placing a dilute solution of an acid in the boiler to subject the interior of the boiler walls for a certain period of time to the action of the acid whereby deposits on the walls are removed therefrom, flushing the boiler by means of water to remove the acid, and directly displacing the water with mercury liquid whereby the boiler surfaces are protected from airby the immediate replacement of the water by the mecury as the water is separated from said surfaces.

5. The method of cleaning a mercury boiler which comprises filling the boiler with a dilute solution of an acid to the normal liquid level in the boiler for removing deposits from the walls of the boiler, flushing the boiler with water and simultaneously heating the boiler to remove the acid and deposits from the boiler, replacing the water with mercury liquid, and drying the boiler by the application of heat to remove the remaining water therefrom.

6. The method of cleaning a mercury boiler having heating tubes which comprises filling the boiler with a dilute acid solution to the normal mercury liquid level in the boiler to remove deposits from the walls of the boiler, flushing the boiler with water and simultaneously heating the boiler until the acid is removed from the boiler, replacing the water with mercury, and heating the boiler to a temperature intermediate the boiling temperatures of water and mercury to remove the remaining water therefrom.

7. The method of cleaning mercury boilers which comprises pouring a cleaning solution into the boiler for removing deposits from the boiler walls, flushing the boiler with water, directly displacing the water with mercury liquid, and drying the boiler whereby the boiler surfaces are protected from air by the immediate replacement of the water by the mercury as the water is separated from said surfaces.

8. The method of cleaning a mercury boiler which comprises slowly heating the boiler and maintaining a vacuum to evaporate and remove the mercury liquid contained therein, pouring a cleaning solution into the boiler to remove deposits on the walls of the boiler, flushing the boiler with water to remove the cleaning solution, and replacing the water with mercury.

9. The method of cleaning mercury boilers which comprises pouring a dilute solution of acid into the boiler, flushing the boiler with a dilute solution of a base to neutralize and remove the acid, flushing the boiler with water, and directly displacing the water with mercury whereby the boiler surfaces are protected from air by the immediate replacement of the water by the mercury as the water is separated from said surfaces.

10. The method of cleaning mercury boilers which comprises pouring a dilute solution of acid into the boiler, flushing the boiler with a dilute solution of ammonia to neutralize and remove the acid, flushing the boiler with water, and directly displacing the water with mercury whereby the boiler surfaces are protected from air by the immediate replacement of the water by the mercury as the water is separated from said surfaces.

11. The method of cleaning a mercury boiler which comprises pouring a dilute solution of acid into the boiler, flushing the boiler with water, adding an alkaline substance to the last part of water, and directly displacing the water and the alkaline substance with mercury whereby the boiler surfaces are protected from air by the immediate replacement of the water by the mercury as the water is separated from said surfaces, the alkaline substance preventing oxidation of the boiler walls during the displacing of the water with mercury.

12. The method of cleaning mercury boilers which comprises pouring a pickling solution including a pickling inhibitor into the boiler, flushing the boiler with water, and directly displacing the water with mercury whereby the boiler surfaces are protected from air by the immediate replacement of the water by the mercury as the water is separated from said surfaces.

ANTHONY J. NERAD. BURT L. NEWKIRK.

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