US1973426A - Apparatus for the degreasing of materials by means of volatile solvents - Google Patents

Description

Sept. 11, 1934. w. BOOTH an; I 1,973,426

APPARATUS FOR THE DEGREASING OF MATERIALS BY MEANS OF VOLATILE SOLVENTS Filed Nov; 8, 1953 g WrSMrpEdwizmfiBQQl/L Joseph Sw g? Patented Sept. 11, 1934 PATENT oer-"ice APPARATUS FOR THE DEGREASING OF MATERIALS BY MEANS OF VOLATILE SOLVENTS William Edward Booth and Joseph Savage, Runcorn, England, assignors to Imperial Chemical Industries Limited,

Britain Application November 8,

a corporation of Great 1933, Serial No. 697,226

In Great Britain November 7, 1932 6 Claims.

This invention relates to apparatus for degreasing by means of the vapour of volatile solvents such as trichlorethylene.

It is well known to degrease metal 'goods by means of the vapour of volatile solvents in apparatus provided with cooling surfaces which may serve to provide a shower of freshly condensed liquid solvent-for the treatment of the goods or to control the level of the solvent vapour. Such processes and the apparatus in which they are being carried out. usually provide for the vaporization of the liquid solvent from a sump into which it drains from thegoods and from the cooling surfaces.

The solvent draining from the goods carries down with it the oily matter on the goods and often a considerable amount of solid impurities which have adhered to the surface of the goods being treated. The impurities accumulate in the sumpand the vaporization of the solvent, particularly as a result of the oily matter, is gradually rendered slower and more difficult.

Previously it has been customary to maintain the rate of-evaporation of the solvent from the sump byincreasing the temperature of the oil and solvent in the sump. Eventually, however, a point is reached beyond which it would be inadvisable to increase the temperature because of the risk of decomposing the solvent,,and consequently the rate of vaporization of the solvent from the sump decreases until it is extremely dif-. ficult to effect the degreasing and because of the slowness the degreasing process becomes relatively uneconomim At this stage degreasing is stopped, the apparatus allowed to cool and the sump cleaned, the accumulated oil and solid imto collect the condensate from the cooling coils.

When the apparatus is being used for degreasin'g, the condensate collecting in the gutters overflows to the sump. there to mingle with the solvent draining from the material under-treatment. To enable the apparatus to act as a still, arrangements are made whereby the condensate 1n the gutters may be drawn off outside the apparatus. The apparatus is used in this manner when the limiting concentration of oil in the sump has been reached, no material being degreased and its sole function being that of a still. The residual oil has to be removed from the sump at the con clusion of the distillation. In so far as this method of working does away with the necessity 'of a separate distillation vessel, it isa marked im-' provement on the method first described but it still does not obviateinterrupting the working of the apparatus from time to time in order to separate the solvent and accumulated oil, and there also remains the disadvantage of a gradual decrease in the rate of degreasing.

The present whereby a constant rate of vaporization of the solvent and consequently a constant rate of degreasing can be maintained. It may also be adapted to provide apparatus in which it is unnecessary to interrupt a series of degreasing operations in order to distil on the solvent from the accumulated oil and to remove oil from the sump of the apparatus.

Accordingly, in degreasing by means of the vapour of-volatile solvents, one feature of the invention comprises collecting separately the condensed solvent draining from the materials under' treatment and a substantially pure condensate which has not been in contact with the oily or greasy material, returning the separate condensates to separate sumps or reservoirs and heating the liquid in both sumps to maintain the supply of degreasing vapour. ,In carrying out the invention we may, advantageously, heat the liquor in the impure solvent sump to main tain it at a temperature such that :the solvent flowing in is vaporized'practically instantaneously, while heating the substantially pure solvent in the other sump to maintain a sufiicient supply of vapour to effect the degreasing of the materials being treated. The residual oily liquor from the apparatus is purged as required, prefinvention provides apparatus the degreasing chamber, and means for collecting clean solvent condensed by the cooling surfaces and for conveying it to another sump, also provided with heating means 'and adapted to a gutter or trough is placed to collect condensate furnish solvent vapour to the degreasing chamthis sump may be provided.

her. Advantageously, means are also provided whereby liquid may be removed continuously from the sump in which the solvent draining from the material is collected while still'main- -into two sumps by means of a dividing wall.

Over the sufnp designed to receive the substantially pure solvent is fitted a roof or cover connected-to the dividing wall and the walls of the apparatus: the flow of liquid from one sump to the other being effectually prevented. The roof is provided with portsadjacent the walls of the vessel and is also arranged to slope upwardly from the dividing wall to the parallel wall of the vessel in order to act as a collector for solvent draining from the material treated. At a short distance above the sumps a ledge is placed around the inside of the vessel. This ledge serves to screen the above mentioned ports in thesump roof and at the same time may serve asa support for the material to be degreased. This material may actually be carried on a grid orin a perforatedcontainer which rests on the ledge, or, if convenient, it may be carried on a perforated Cooling coils 10 with inlet and outlet for cooling water are fixed round the walls in the upper part of the apparatus to condense solvent vapour and thereby to control its height and prevent its escape from the plant. Immediately below the coils is a gutter 11 placed to collect the condensate from the coils and to provide for its return by means of the pipe 12 to the clean solvent sump2. The pipe 12 is preferably provided 'with a threeway cook 18 which passes the solvent from the gutter 11 to the sump 2 when the plant is operating normally as a degreaser. If for any reason it is desiredto utilize the plant as a still, the cock 18 may be set to pass clean solvent from the gutter 11 to a storage vessel by means of the.

pipe 19. This use may arise if a complete cleansing or overhaul of the plant is at any time found to be necessary. The heating of the solvent in the sumps is effected by the gas burners 13 and 14 which are subject to the thermostatic controldevices 15 and 16, in order to avoid the possibility of over-heating. The trapped outlet pipe 1'7 from r container supported by another ledge or h8g8- run -oi'f cock on the impure solvent sump 3 may brackets, or by means external to the vessel. In the upper part of the vessel leaving a suiliciency of space. for the goods to be treated, cooling coils with appropriate connections for a supply 'of cooling liquid are arranged round the walls to control the height of the solvent vapour durtl'le degreasing operation. Below the coils from the coils for conveyance by means ofa pipe or pipes to the roofed sump. Heating means are provided for each sump and this may be a set of steam coils, an electric heater or a gas burner as is convenient. We also find it advantageous to incorporate thermostatic control devices for the heating means? particularly in connection with the impure solvent sump when the heating is effected by means of electricity or gas. A further advant ous modification is the provision of-a constant level over-flow device connected to the impure solvent sump. and designed to maintain a volume of liquid therein while permitting the overflow of oily liquor recovered from the material treated.

The accompanying drawing illustrates diagrammatically one form of the degreasing apparatus according to the invention, Figure 1 being a sectional elevation and Figure 2 a plan.

In the drawing the rectangular vessel 1 is formed at the bottom into separate sumps 2 and .3 by means of the dividing wall 4. The sump 2 is designed to contain the substantially pure solvent and to receive the clean condensate. It is providedwith an inclined roof 5 which permits any greasy solvent dropping from the goods to on which goods to be degreased can be supported.

be used to withdraw oily materal intermittently,

and in this case the outlet pipe 17 maybe dispensed with. v

Before commencing the degreasing operation a sufllcient quantity of volatile solvent, for example trichlo'rthylene, is charged into the apparatus. The necessary vapour for degreasing is then furnished by heating the solvent and the height of the vapour in the upper portion of the vessel is automatically controlled bythe cooling coils 10 to which cooling liquid, suitably-water, is supplied. When starting degreasing with a clean plant it is not essential that the initial charge of clean solvent should beconfined to the sump 2. This course is, however. usually adopted in order that the normal conditions under which the plant will work shall be reached as quickly as possible. To accelerate the attainment of these normal conditions we also find that it is advantageous to charge into the sump 3 a quantity of oil which is also heated. In this way. the oil forms a reservoir for heat and provides for the-rapid evaporation of solvent draining into the sump 3 when degreasing commences. Materials to be degreased are put in the vessel in any convenient manner and are suitably supported on the grid 9 or in a perforated basket adapted to rest on the ledge 8 around the inside of the vessel, left the necessary length of time to effect degreasing, removed and replaced by a further batch to be treated. The degreasing of the materials is effected by the condensation thereonof the solvent which subsequently drains ofi carrying with it dissolved oil to collect in the impure solvent sump. Any solvent carrying oil which drops on to the roof 5 of the pure solventrsump naturally flows into the impuresolvent sump by reason of the slope of the roof. The impure solvent sump is maintained at such atemperature that substantially all the solvent flowing into it is vaporized almost instantaneously. A suitable temperature for this purpose is about C. Preferably thermostatic devices are used to control the temperature when gas or electricity is used as the source of heat. When steam is used it is supplied to the coils at a suitable pressure sufficient to maintain the desired temperature. The pure solvent in the other sump 2 is kept constantly boiling in order to maintain a sufficiency of vapour to replace that condensed in the degreasing operation and on the coils controlling the height of the vapour. liquid solvent will, of course, be substantiallly maintained by the flow back from the cooling coils, but it will be necessary from time to time to replenish with fresh solvent to replace a small amount of wastage and loss including solvent which is associated with the oily liquor removed from the apparatus.

It will be understood that the apparatus described is illustrative only of one form falling within the scope of the invention. The invention may, for example, be applied to degreasing in which the materials to be treated are moved through a zone of solvent vapour, with or without simultaneous treatment with liquid solvent,

'or to degreasing in which the materials are treated in succession with liquid solvent and vaporized solvent. Modifications of the apparatus include a funnel shaped device as collector for the impure solvent, and a collector and sump in the form of a shallow tray provided with heating means and situated immediately beneath the materials treated. Cooling coils adapted to supply a shower of freshly condensed solvent on the materials treated may also be incorporated in the apparatus.

What is claimed is:

1. An apparatus for degreasing materials by means of the vapour of volatile solvents, comprising a degreasing chamber, means for supporting materials to be degreased within the chamber, cooling surfaces above the normal level of the materials to be treated, a sump in the bottom of said degreasing chamber for collecting condensed solvent draining from the materials, said sump being provided with heating means and being adapted to furnish solvent vapour to the degreasing chamber, a second sump, constructed and ar ranged to prevent access thereto. of condensed solvent'from the materials being degreased, in the bottom of said' degreasing chamber, and means located below said cooling surfaces for collecting clean solvent condensed by the cooling surfaces and for conveying it to said second sump,

openings to allow of the passage of solvent vapour The volume of pure from the sump below, which openings are shielded from condensate dripping from the materials.

3. An apparatus as claimed in claim 1, in which the degreasing chamber takesthe form of a rectangular vessel the bottom portion of which is divided into two sumps by means of a dividing wall, over one of which sumps is fitted a sloping roof adapted to catch condensate dripping from the materials under treatment and to cause it to flow into the other sump, the said roof having openings to allow of the passage of solvent vapor from the sump below, which openings are adjacent the walls of the chamber and are shielded from condensate dripping from the materials by a peripheral ledge servingas a support for the materials to be degreased.

4. Apparatus for degreasing materials by means of the vapor of volatile solvents, comprising a vessel formed to provide two separate compartments in the bottom thereof adapted to receive andvaporize solvent and a degreasing chamber,

above said compartments, cooling surfaces in said degreasingchamber, heating means for said compartments, both of said compartments communicating with said degreasing chamber and being adapted to furnish solvent vapors thereto, one of in said degreasing chamber, and means for col constant-level liquid over-flow device arranged,

to maintain a constant level of liquid in" said compartment while permitting overflow of oily liquid.

6. Apparatus for degreasing materials by means of the vapor of volatile solvents comprisinga degreasing chamber, cooling surfaces in said degreasing chamber above the normal level of the materials to be degreased, means for supporting materials to be degreased within said chamber, means supplying solvent vapors to said degreasing chamber and receiving condensed solvent draining from the materials being treated in said degreasing chamber, additional means separate from said first-mentioned means for supplying solvent vapors to said degreasing chamber, said additional solvent-supplying means being constructed and arranged so that access thereto of condensed solvent from the materials being treated is prevented, and means for collecting solvent condensed by said cooling surfaces and for delivering it to said additional solvent-supplying means.

A 'WILLIAM EDWARD BOOTH. JOSEPH SAVAGE.

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