Method and System for Recycling Washing Liquids and the Heat Contained Therein

The invention relates to a method for recovering and recycling of washing liquids and the heat contained in the washings discharged from metal surfacing processes, and is concerned with a system for effecting such a method as well.

In the conventional chemical metal surface treatment processes, one of which is typically illustrated in FIG. 1, the quality of the cold washing water and the hot water in tanks 16 and 1 has to be kept constant by supply of a given amount of water and its discharge from the tanks involved by overflow means. More specifically, fresh steam 2 is fed from a boiler directly or indirectly into hot water washing tank to maintain the temperature therein, and the resulting hot water is discharged as such, i.e., without being subjected to any heat recovery treatment. This poses a problem in connection with the effective use of water resources and energy savings.

This invention has been accomplished with a view to providing a solution to the aforesaid problem.

A main object of this invention is therefore to provide a method and system which combine recycling of washing liquids with heat recovery.

Another object of this invention is to stabilize the quality of water supplied into and held in water and hot water washing tanks for the purpose of preventing deterioration of the metal products to be treated due to variations in quality of the water contained therein.

According to one aspect of the invention, there is provided a method for recovery and recycling of the washing liquid and the heat contained in the washings discharged from the chemical metal surface treatment process, which comprises permitting cold water (about 40.degree. C.) discharged from a cold water washing tank to exchange heat with hot (about 80.degree. C.), pure water before its introduction into a hot water washing tank, filtering the washings discharged from the hot water washing tank, subjecting the resulting filtrate to heat exchange and ion exchange to obtain pure water, and feeding the pure water back to the cold water washing tank.

According to another aspect of the invention, there is provided a method for recovery and recycling of the washing liquid and the heat contained in the washings discharged from a metal surface treatment process, which comprises allowing hot water discharged from a hot water washing tank to exchange heat with cold, pure water before its introduction into the cold water washing tank, filtering the liquid discharged from said water washing tank, subjecting the resulting filtrate to ion exchange to obtain pure water, heating the obtained pure water through heat exchange with said hot water, and feeding the thus heated water back to said hot water washing tank.

According to still another embodiment, there is provided a method for recovery and recycling of the washing liquid and the heat contained in the washings discharged from a metal surface treatment process, which comprises subjecting hot water discharged from a hot water washing tank for storing the second washings obtained in said process to heat exchange with cold, pure water to obtain cold water, introducing the obtained cold water into a cushion, buffer or holding tank together with impurities-containing cold water coming from a water washing tank for storing the first washings obtained in said process, filtering the liquid contained in said cushion tank, subjecting the resulting filtrate to ion exchange to obtain pure water, and heating a part of said pure water through heat exchange with said hot water for its feedback or recycling to said hot water washing tank while feeding another part of said pure water to said water washing tank without application of heat.

The above-mentioned and other objects and advantages of the invention will become apparent from a reading of the following detailed description with reference to the drawings, in which:

FIG. 1 is schematically illustrative of a typical washing device used with the prior art metal surface treatment process;

FIG. 2 is schematically illustrative of one embodiment of the system of this invention for recycling of washing liquids and heat contained in the washings discharged from the metal surface treatment process; and

FIGS. 3 and 4 are schematically illustrative of second and third embodiments of the invention.

Referring now to FIG. 2, a hot water washing tank 1 includes therein a fresh steam inlet pipe 2, and has a hot water recovery pipe 3 located on one side and a hot water discharge pipe 4 on the other side. The other end of pipe 4 is then in communication within cushion tank 5.

The cushion tank 5 includes therein a water suction pipe 6 which extends through a pump 7 to a filter 8.

The filter 8 communicates with a filtrate reservoir 10 via a discharge pipe 9.

The filtrate reservoir 10 is in communication with a pipe 12 having a pump 11 on its way, which pipe passes through heat exchanger 13.

Part of the pipe 12 which leaves the exchanger 13 terminates in an ion exchanger 14. A cold water recovery pipe 15 then connects the ion exchanger 14 to cold water washing tank 16.

The cold washing tank 16 is connected on its one side with one end of a cold water discharge pipe 17 which is, in turn, connected on its other end within a cushion tank 18.

Communication is made between the cushion tank 18 and a pipe 19 passing through the heat exchanger 13, said pipe 19 having a pump 20 on its way. The pipe 19 is also connected with the hot water recovery pipe 3.

In what follows, the inventive method of recovery and recycling of the washing liquids and the heat contained in the washings will be explained with reference to the thus arranged recycling system shown generally at A.

In the process for repeating a cycle wherein the surface of a metal to be treated is washed in the hot water washing tank 1 and, then, in the cold water washing tank 16, circulation of a washing liquid is first effected through the system A.

The cold water washing tank 16 discharges contaminated cold water (ca. 40.degree. C.) which passes through the pipe 17, cushion tank 18, and pipe 19 and exchanges heat with hot, pure water in the heat exchanger 13 with the resulting hot water (ca. 80.degree. C.) being fed into the hot water washing tank 1.

The tank 1 discharges hot water containing contaminants into the cushion tank 5 through the pipe 4. Subsequently, the hot water is supplied from the suction pipe 6 into the filter 8 via the pump 7, where it is filtered off. The resulting filtrate is discharged into the reservoir 10 via the pipe 9.

The filtrate which leaves the reservoir 10 is supplied into the heat exchanger 13 via the pipe 12 by means of the pump 11, where it exchanges heat with cold water. The filtrate which is now adjusted to a temperature suitable for ion exchange is fed into the ion exchanger 14.

The ion exchanger 14 permits removal of cations (Ca.sup.++, Na.sup.+, etc.) and anions (S0.sub.4.sup.-- etc.) contained in the filtrate through ion exchange until it is converted into pure (salt-free) water.

Cold water (approx. 35.degree. C.) which is now converted into pure water through ion exchange is fed back into the cold water washing tank 16 through the pipe 15 for recovery. For circulation of the washing liquid, such operations are repeated.

The objects of the present invention can also be achieved by starting with the hot water discharged from the hot water washing tank in the above-mentioned recycling process of washing liquids and heat. In what follows, this will be explained with reference to FIG. 3.

A hot water washing tank 101 includes therein a fresh steam inlet pipe 102, and has recovered hot water make-up pipe 103 located on one side and a hot water discharge pipe 104 on the other side. The other end of the pipe 104 is in communication within a cushion tank 105.

The cushion tank 105 communicates with one side of cold water washing tank 108 via a pipe 107 passing through a heat exchanger 106. A pump 109 is mounted on the pipe 107 between the tank 105 and the heat exchanger 106.

A cold water discharge pipe 110 communicates at its one end with the other side of the washing cold tank 108 and at its other end with a cushion tank 111.

The cushion tank 111 includes therein a water suction pipe 112 which terminates in a filter 114 via a pump 113.

The filter 114 communicates with a filtrate reservoir 116 via a discharge pipe 115.

The reservoir 116 communicates with an ion exchanger 119 via a pipe 118 having a pump 117 on its way.

The ion exchanger 119 communicates with a pipe 120 passing through the heat exchanger 106, said pipe 120 being connected with the hot water recovery pipe 103. In this way the washing liquid and heat recycling system, generally shown at A, is assembled.

Operation of the thus arranged system A will be explained.

In the operation for repeating a cycle wherein the surface of a metal to be treated is washed in the cold water washing tank 108 and, then, in the hot water washing tank 101, circulation of a washing liquid is first effected through the system A.

The hot water washing tank 101 discharges contaminated hot water (ca. 80.degree. C.) which passes through the pipe 104, cushion tank 105 and pipe 107 and exchanges heat with cold, pure (salt-free) water in the heat exchanger 106 with the resulting purified cold water (ca. 40.degree. C.) being fed into the cold water washing tank 108.

The tank 108 discharges cold water containing contaminants into the cushion tank 111 through the pipe 110. Subsequently, the cold water is supplied from the suction pipe 112 into the filter 114 via the pump 113, where it is filtered from contaminents. The resulting filtrate is discharged into the reservoir 116 via the pipe 115.

The filtrate adjusted to a temperature suitable for ion exchange, leaves the reservoir 116 is supplied into the ion exchanger 119 via the pipe 118 by means of the pump 117. This ion exchanger functions in the same manner as mentioned in connection with the ion exchanger 14.

Cold water (approx. 35.degree. C.), now converted into pure (salt-free) water through ion exchange, is fed into the heat exchanger 106, where it exchanges heat with the above-mentioned hot water (approx. 80.degree. C.) containing contaminants, and becomes pure water (approx. 75.degree. C.). This pure water is then brought to a higher temperature by fresh steam or other means.

Better results are obtained if some modifications are made to the foregoing second embodiment. This will now be explained with reference to FIG. 4.

As will seen from FIG. 4, the third embodiment is similar to the second embodiment except for the provision of a bypass pipe 122 extending from between the heat exchanger 106 and the ion exchanger 119 into the cold water washing tank 108. If desired, a filter 121 may be disposed between the pump 109 and the heat exchanger 106 to prevent the exchanger 106 from being scaled or corroded.

The third embodiment works in a manner that is explained with reference to the second embodiment, except that a part of pure water obtained by ion exchange is fed back to the hot water washing tank 101 via the heat exchanger 106, while another part of pure water is fed back to the cold water washing tank 108 through the bypass pipe 122. More specifically, an amount of cold water (ca. 35.degree. C.) obtained by ion exchange and converted into pure water is supplied into the heat exchanger 106, where it exchanges heat with the hot water (ca. 80.degree. C.) containing impurities and becomes pure water having a temperature on the order of about 75.degree. C. This pure water is then fed back to the hot water washing tank 101 and brought to a higher temperature by fresh steam or other means. The remaining amount of pure water is fed back to the cold water washing tank 108 through the bypass pipe 122.

Reference will be made to the action and effect of the invention. With the embodiments according to the invention, a washing liquid is recycled many times with no need for a supply of a constant amounts of extra water as required in the prior art. This results in water savings and efficient washing. Alternate use of the cold water in the cold water washing tank and the hot water in the hot water washing tank for heat exchange also leads to simplification of in the equipment involved and decreases in the amount of steam introduced into the hot water washing tank, and is preferable in view of energy savings. In addition, the quality of the washing water in both tanks can be stabilized to prevent deterioration of the metal products to be treated. As there is no fear that clogging of the filtering material may take place, the operation for washing it can be simplified.

According to the invention, any steps for frequent supply of fresh water are dispensed with. There is also no need for providing the cold water and hot water washing tanks with effluent vessels or sumps for the purpose of allowing frequent discharge of washings or of emptying the tanks. Therefore, the inventive system can be made compact and operated in a simple manner and in a good working environment where there is little or no risk of washing water leaks. Furthermore, the adjustment of washing water to a temperature suitable for ion exchange (Ca 35.degree.-40.degree. C.) is done through heat exchange or the like, and the washing of the filtering material is considerably reduced.

Especially with the third embodiment of the invention, it is feasible to simultaneously feed pure liquids back to both the hot water washing tank and the cold water washing tank. This assures that the quality of the liquids contained in each tank is kept in a satisfactory state during operation of the system, leading to improvements in the quality and accuracy of the metal product treated.

While the invention has been described in detail and with reference to the specific embodiment thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.