Vapor compression liquid treating system

A liquid containing a solvent to be evaporated is fed to a concentration chamber which is fluidly connected to an evaporation chamber maintained at a reduced pressure. A vapor compression means withdraws solvent vapor from the evaporation chamber, compresses the vapor and forces the compressed vapor to a liquification chamber. Regulator means responsive to the density of the liquid remaining within the concentration chamber will regulate the rate of solvent evaporation to provide a concentrate suitable for recycling. A method of operating the still of this invention utilizes the technique of increasing the compressor capacity until the compressor begins to surge and then reducing the capacity a fixed amount to provide the desired efficiency.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
In one aspect, this invention relates to vacuum distillation systems. In 
another aspect, this invention relates to closed loop waste treating 
systems. In yet a further aspect, this invention relates to methods of 
using distillation systems. 
2. Description of the Prior Art 
Prior art distillation systems wherein a variable speed compressor is used 
to put energy into a vapor which is in turn condensed to give off latent 
heat of vaporization to a distilland are known in the art. One example of 
such a system is shown by U.S. Pat. No. 2,446,880. These systems have been 
primarily used for water desalinization and operate at temperatures near 
or even above the boiling point of water at atmospheric pressure. 
Such systems are not desirable for distilling fruit juices or plating 
solutions; since they must be concentrated at temperatures well below the 
boiling point of water to prevent degradation of the organic materials 
present. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved method of 
controlling the vapor compression process. The vapor compression system of 
this invention has an evaporation chamber maintained at a reduced 
pressure, a concentration chamber for holding the distilland to be 
concentrated, a density measuring means for measuring distilland density, 
and an evaporation surface connecting to the concentration and evaporation 
chambers. This configuration allows the distilland to be retained within 
the concentration chamber until the desired distilland concentration 
measured as a function of density is obtained. 
As a further feature of this invention, the compressor capacity is 
increased until the compressor reaches a surge condition and the 
compressor capacity is reduced an incremental amount to bring the 
compressor into the desired operating range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A typical plating schematic using a vapor compression still is shown in 
FIG. 1. Parts to be plated are placed in a plating tank 12 which contains 
a solution of ions to be deposited on the parts as a metal layer. After a 
metal layer has been deposited on the parts, the plated parts are moved 
successively to rinse tanks 14, 16, 18 where any plating solution clinging 
to the plated part is rinsed off. 
A substantial amount of plating solution, containing valuable metal ions 
and organic additives, is carried into the rinse tanks. Also, some water 
is carried from tank to tank by the parts as they are rinsed. The carry 
over and evaporation from the rinse tanks depletes the water in the rinse 
tanks and the concentration of plating solution will steadily rise, 
especially in the first rinse tank 14. 
A portion of the water in the first rinse tank 14 is periodically withdrawn 
from the bottom of the tank and sufficient water from the second tank 16 
is transferred via line 15 to refill tank 14. The tank 16 is refilled from 
tank 18 via line 17 and tank 18 is in turn filled by purified water from a 
vapor compression still 20 via line 19. Additional water can be added from 
an outside source of fresh water 21 when needed. 
As shown, the rinse water or distilland from the first rinse tank 14, is 
withdrawn at outlet 22 by opening valve 24. The contaminated rinse water 
is conveyed by a pipe 26 to a heat exchanger 28 where the rinse water 
extracts some heat from purified water condensed in the vapor compression 
still 20. The preheated rinse water passes through a three-way valve 30 
and is fed to the vapor compression still from the rinse water. The rinse 
water is concentrated to a density suitable for return to the plating tank 
12. The concentrated solution is withdrawn from the concentration chamber 
through a valve 32 and pumped to the plating tank 12 via a line 34. 
The pure water resulting from the vapor compression cycle is withdrawn 
through valve 36 into the heat exchanger 28 via line 38 and then is 
returned to rinse tank 18 by line 19. 
If desired, the vapor compression system can be used to purify water before 
it enters the plating cycle. Treatment of the water before it enters the 
system removes the calcium, magnesium, and other undesired metal ions 
which are present in every source of water. These metal ions will 
concentrate in the plating bath as water is lost and settle out as solid 
salts to form a sludge at the bottom of the tank 12 or remain in the 
plating solution. In either case, the increasing concentration of 
undesired metal ions reduces plating efficiency. Eventually the plating 
solution must be discarded, resulting in a loss of valuable metal ions in 
the solution discarded, or the sludge must be removed from the plating 
tank requiring that plating operations be suspended. Accumulation of this 
sludge would be particularly pronounced where the process cycle is a 
closed loop as shown. Purification of the incoming fresh water would 
lessen or eliminate this problem. 
FIG. 2 shows a detailed view of one vapor compression apparatus useful in 
the practice of this invention. The operation of this unit is described 
with reference to plating rinse water. The system could also be used to 
treat other liquids such as fruit juices, organic solvents or sea water. A 
generally cylindrical, vertically oriented housing 39 defines an 
evaporation chamber 40 which collects vaporized water from the inside of 
the tubes 54 located at one end of the housing near a compressor 42. The 
compressor 42 comprises generally a compressor wheel 43, volute 45 and 
driving means 46. As shown, the driving means is an electric motor 47 
mounted on a bracket 48 attached to the housing 39. The motor 47 drives a 
V-belt drive 49 which in turn rotates the compressor wheel 43. The 
compressor wheel 43 withdraws vapor from the evaporation chamber 
maintaining the evaporation chamber at a reduced pressure e.g., 0.5 to 1.5 
pisa. As shown, cross-tubes 50 transport compressed vapor from the volute 
45 to a condensation-heat exchanger chamber 52. 
At the lower end of the housing 39, distal the compressor 42, are a number 
of concentration chambers (three being shown) 44a, 44b, 44c which are 
filled with rinse water to be concentrated or incoming fresh water to be 
purified. Each concentration chamber is fluidly connected to the 
evaporation chamber 40 by an evaporation surface. As shown, the fluid 
connection is by means of capillary tubes 54 which extend from the lower 
portion of their respective concentration chambers and terminate in the 
plate 56 which forms the floor of the evaporation chamber 40. In general 
there will be a plurality of tubes extending from each concentration 
chamber into the evaporation chamber, only one tube per concentration 
chamber being shown for clarity. The interior walls of the capillary tubes 
54 are wet by the liquid being concentrated and provide a large surface 
area for the formation of water vapor which passes into the evaporation 
chamber 40. 
Sensing means 58a, 58b, and 58c are installed in each concentration chamber 
to measure the concentration of the remaining liquid. As shown, the 
various sensing means generate an electrical signal which is fed to a 
control means 60. The control means 60 activates the three-way valve 32 so 
that the concentration chambers can be emptied when the liquid in the 
chambers reaches the desired concentration. In one aspect of this 
invention the concentration of the remaining liquid is determined by 
measuring its density. Suitable density measuring devices are known in the 
liquid measuring art. One general method of density measurement, which 
could be used in practicing this invention, is displacement measurement 
using a float. Such devices operate by submerging a float in the liquid to 
be measured. The float's movement up and down within the liquid generates 
a continuously variable signal proportional to the density of the 
surrounding liquid. A full description can be found in Chemical Engineers 
Handbook, 5th Ed., McGraw-Hill, New York, 1973, especially pages 22-48, 
and 49, the disclosure of which is incorporated herein by reference. 
In general, pumps (not shown) would be associated with the various valves 
to move the liquid within the system as needed. The chamber would be 
replenished via valve 30 with more liquid to be concentrated as needed. 
A large diameter vertically oriented duct 51 extends longitudinally along 
the middle of housing 39. Overflow liquid from tubes 54 flows into the 
duct and down into a reservoir 65. 
The liquid in reservoir 65 can in turn be pumped by a pump 66 through a 
valve 68 to the inlet of valve 30, returning the overflow liquid into the 
concentration chamber. 
OPERATION 
In general, as with stills of this type, vapor from the liquid being 
treated will be generated on an evaporation surface. The vapor generated 
will be drawn into a compressor, compressed, and the compressed vapor is 
condensed. Generally the vapor is condensed so that the latent heat of 
condensation is transferred to the liquid being treated thereby creating 
more vapor to be compressed. 
In greater detail, vapor exiting from the upper end of tubes 54 will enter 
the evaporation chamber 40, passing over the cross tubes 50. As the vapor 
passes the cross tubes 50, it will remove some heat from the cross tubes 
which super heats the vapor and lowers the heat in the compressed vapor. 
The rising vapor enters a liquid carrier 74 which will remove any 
remaining liquid droplets entrained in the vapor stream. The barrier is 
shown as a screen but can be other materials known in the art, one barrier 
material being porous agglomerated plate. 
The vapor, free from liquid, enters the housing surrounding the rotating 
compressor wheel 43, is accelerated by the wheel and is pushed into the 
volute 45 where the vapor's velocity decreases and the pressure increases. 
The vapor from volute 45 enters the cross tubes 50 and passes through the 
tubes to a plenum 76 located within the housing. From the plenum, the 
compressed vapor enters a variable capacity heat exchange chamber. The 
heat exchange chamber comprises the chamber 52 defined by the plate 56, 
the upper surface of concentration chamber 44a, and the housing 39. Vapor 
entering the chamber 52 will be exposed to the exterior walls of the tubes 
54 and, being at a higher temperature and pressure than the liquid inside 
the tubes, will condense to form a liquid. As shown, the chamber 52 
contains a quantity of liquid and a vapor filled space 66 above the 
liquid. The heat transfer to the capillary tubes is different for the 
vapor filled phase and the liquid phase. By varying the liquid level 
within the heat exchange chamber 52, the amount of heat transferred to the 
liquid within the tubes 36 and thus the amount of additional vapor created 
can be controlled. The heat transfer and thereby the amount of vapor can 
also be controlled by varying the height of solvent within the tubes, a 
lower liquid level resulting in a lower heat transfer. 
Of course, control of the vapor compression still involves several 
variables in addition to the liquid level in the chamber 52 or tubes 54. 
With a given compressor wheel, the amount of liquid withdrawn from the 
concentration chambers will vary as a function of: compressor wheel speed, 
inlet geometry and guide vane angle. In general, if the liquid level in 
the heat exchange chamber is increased, the amount of heat available to 
evaporate solvent and concentrate liquid is decreased. 
The inlet geometry can be changed to vary the compressor's operating 
capacity. Such variable inlet geometries are well known in the art and a 
further description is omitted in the interest of brevity. 
Because of changes in the distilland or variations in the production 
process to which this system is attached changes are necessary from time 
to time. One method of operating the compressor of this system is to 
increase the compressor capacity, such as by increasing compressor wheel 
speed until the compressor crosses the surge line and begins to surge. The 
compressor capacity could then be reduced by a fixed amount, such as by 
changing compressor speed or inlet geometry, to bring the capacity to the 
desired point on the efficiency curve. The operating efficiency curves are 
determined by the variables present in the system each system being 
individualistic but the operating characteristic curve as easily 
calculated or emperically determined. Such charts showing efficiency 
islands as a function of pressure ratio versus flow at a constant impeller 
tip speed are so well known that a detailed example is omitted. One 
example of a centrifugal compressor performance chart can be found in Gas 
Turbines, Sorenson, Ronald Press Co., New York, 1951, especially page 267. 
Ordinarily causing a centrifugal compressor wheel to surge would not be a 
viable means of controlling a process. However, because the compressor 
wheel is operating at a reduced pressure, the amount of energy applied to 
the wheel during surge is minimal. Using the surge point of the compressor 
as a control measurement provides a quick and easy method of determining 
the operating conditions at a given time since the pressure ratio changes 
markedly when the compressor surges. Pressure sensing devices are well 
known in the art and a detailed description is omitted in the interest of 
brevity. The surge control can be used in combination with the variable 
heat exchanger to further increase the efficient operating range of the 
system. 
The operating steps detailed above could be performed by a microprocessor 
which would receive relevant data and determine the operating condition of 
the system by comparison with a predetermined performance chart. If the 
system needed correction, the microprocessor would be programmed to drive 
the system into the surge condition and adjust the compressor capacity as 
discussed hereinbefore. 
Where the liquid in one of the concentration chambers 44a, 44b, and 44c 
reaches the desired concentration, the sensing means in the associated 
chamber will activate the control means 60 which in turn activates the 
valve 32 to empty the concentration chambers. The emptied chamber is 
refilled and the process continues. 
Various modifications and alterations of this invention will become obvious 
to those skilled in the art without departing from the scope and spirit of 
this invention. For example, the still of this invention can be used to 
concentrate fruit juice and for disalinization of water in addition to 
treating plating rinse water.