Pressurized closed flow cleaning system

A pressurized closed flow cleaning system for cleaning the interior surface of industrial processing equipment. A pressure vessel contains an aqueous cleaning solution including the combination of enzymes and a surfactant. A supply conduit connects the pressure vessel with equipment to be cleaned and serves to supply the cleaning solution to the equipment, while a return conduit connects the equipment to the pressure vessel and acts to return the cleaning solution to the pressure vessel, thus providing a closed flow system. The solution is circulated through the closed flow system by a pump located in the supply conduit and the aqueous solution is heated to a temperature, preferably in the range of about 220.degree. F., to 260.degree. F., by a heat exchanger which is located downstream of the pump. Flow of the heated cleaning solution through the equipment to be cleaned will remove oil and solid contaminants. The system also includes a reverse flow manifold which interconnects the supply conduit and the return conduit and acts to selectively reverse the flow of cleaning solution through the equipment. The solution returned to the pressure vessel is maintained in a relatively quiescent state to permit the oil to settle out as an upper layer in the pressure vessel and an oil drain conduit is connected to the vessel for selectively draining oil from the vessel. The pressure vessel also includes a provision for removing benzene and other hydrocarbon gases from the circulating cleaning solution.

BACKGROUND OF THE INVENTION 
Chemical processing and oil refinery equipment become contaminated during 
use with oil and solid deposits, such as coke or iron sulfide. As the 
processing equipment normally consists of a closed vessel, the typical 
procedure for cleaning the vessel is to circulate a cleaning solution 
through the vessel in an attempt to emulsify the oily materials and 
dissolve the hydrocarbon binders to dislodge the solid particles. The flow 
of the cleaning solution will then act to flush the residue from the 
vessel. 
It has been found that a cleaning solution which includes the combination 
of enzymes and a surfactant is extremely effective in removing oil and 
solid deposits, such as coke or iron sulfide, from industrial processing 
equipment as well as from industrial machinery. Not only is this 
combination of ingredients effective in removing oil and dissolving the 
binder that binds the coke or iron sulfide particles, but it also has the 
advantage that when the residual cleaning solution is maintained in a 
quiescent state, the oil will separate from the water phase, so that the 
oil can be readily removed from the solution. 
It has also been found that the effectiveness of the cleaning solution 
containing enzymes and a surfactant is increased as the cleaning solution 
is heated to an elevated temperature. However, when the temperature 
approaches the boiling point, i.e. 212.degree. F. the solution will boil 
and due to the presence of the surfactant, tremendous quantities of foam 
are generated in the cleaning system. The large quantities of foam can 
cause cavitation of the circulating pump, with the result that the 
cleaning solution cannot be effectively pumped through the equipment to be 
cleaned. 
SUMMARY OF THE INVENTION 
The invention is directed to a pressurized closed flow cleaning system for 
cleaning vessels and other equipment which utilizes an aqueous solution of 
enzymes and a surfactant. In accordance with the invention, the 
pressurized cleaning system includes a pressure vessel that is partially 
filled with an aqueous cleaning solution containing the combination of 
enzymes and a surfactant. As the cleaning solution occupies only a portion 
of the pressure vessel, a headspace is created above the level of the 
solution in the pressure vessel. 
A supply conduit connects the pressure vessel with the equipment to be 
cleaned which may constitutes one or more closed vessels or pieces of 
equipment, and the aqueous solution is pumped trough the supply conduit to 
the equipment by a circulating pump. A return conduit connects the 
equipment to the pressure vessel for the return of the solution to the 
pressure vessel. 
Located in the supply conduit is a heat exchanger, which is employed to 
heat the cleaning solution being supplied to the equipment to be cleaned 
to a temperature generally in the range of about 220.degree. F. to 
260.degree. F. The heated cleaning solution, flowing through the equipment 
to be cleaned at a rate generally in the range of 1000 to 3000 gallons per 
minute will act to effectively emulsify oils and dissolve the binders in 
the coke or ferrous deposits on the internal walls of the equipment, thus 
dislodging the coke or ferrous particles. The dislodged particles will 
then be carried away by the circulating solution and returned to the 
pressure vessel. As the process of the invention utilizes high flow rates, 
the dislodged solid material will be readily flushed from the equipment to 
be cleaned and conveyed to the pressure vessel. 
The pressure vessel includes a weir which divides the vessel into a first 
inlet section and a second outlet section. The return conduit is connected 
to the inlet section and the solid particles in the solution being 
returned to the pressure vessel will tend to settle out in the inlet 
chamber, while the cleaning solution will overflow the weir into the 
outlet section and thus be recycled through the supply conduit to the 
equipment to be cleaned. 
The invention also preferably includes a reverse flow manifold which 
interconnects the supply conduit and the return conduit. The reverse flow 
manifold includes valving which enables the flow through the equipment to 
be cleaned to be selectively reversed. The reversal of flow is 
particularly important when a series of vessels or equipment are to be 
cleaned which are connected in series. 
The invention also includes a provision for periodic blow-down of the solid 
material which has collected in the pressure vessel. In this regard, a 
series of blow-down lines are connected to the lower end of the pressure 
vessel and by momentarily opening the lines, the solid material can be 
discharged from the pressure vessel to a waste storage tank or other 
disposal site. 
As a further feature of the invention, a provision is made to periodically 
remove accumulated oil from the cleaning solution in the pressure vessel. 
As the cleaning solution in the pressure vessel is maintained in a 
relatively quiescent state, the oil in the solution will collect as an oil 
phase on the top of the water phase. An oil drain conduit is connected to 
the pressure vessel at a level communicating with the oil phase, so that 
oil can be periodically withdrawn from the pressure vessel during the 
cleaning operation and discharged to the waste storage tank. 
When cleaning contaminants from refinery vessels, such as fractionators or 
heat exchangers, benzene is often entrained in the cleaning solution, and 
the invention includes a provision to strip the benzene from the cleaning 
solution in the pressure vessel and discharge the released benzene vapor 
to a combustion site 
As the flow system of the invention is pressurized, operating at a pressure 
generally in the range of 30 to 60 psig, the cleaning solution can be 
heated to a temperature well above the boiling point of water without 
generation of foam. Utilizing the cleaning solution at this elevated 
temperature increases the effectiveness of the solution in emulsifying oil 
and removing the solid deposits from the equipment wall. 
The invention also enables the solid residue, oil and hydrocarbon gases, 
such as benzene, to be removed from the pressure vessel while the cleaning 
operation is in progress and there is no release of any contaminants to 
the atmosphere through use of the process of the invention. 
Other objects and advantages will appear in the course of the following 
description.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
The drawing is a diagrammatic representation of the process of the 
invention utilized to clean a series of closed vessels or processing 
equipment, such as used in chemical processing or oil refineries. 
As shown in the drawing, a closed pressure vessel 1 contains an aqueous 
cleaning solution composed of a combination of enzymes and surfactant. The 
cleaning solution can be of the type described in U.S. patent application 
Ser. No. 08/128,061, filed Sept. 29, 1993 now U.S. Pat. No. 5,459,066, in 
which the aqueous solution contains about 1 to 200 ppm of enzymes selected 
from the group consisting of proteases, amylases, lipases, cellulases, and 
mixtures thereof, along with about 30 to 2100 ppm of a surfactant having 
the following formula: 
##STR1## 
where n is 6 to 20. More specifically, the surfactant may be lauryl 
dimethyl amine oxide, stearyl dimethyl amine oxide, myristyl dimethyl 
amine oxide, and mixtures thereof. 
Located in vessel 1 is a weir 2 which extends upwardly from the bottom 
surface of the pressure vessel and divides the vessel into an inlet 
section 3 and an outlet section 4. An outlet line 5 is connected to one 
end of the vessel and communicates with outlet section 4 and the cleaning 
solution contained within vessel 1 is drawn through the outlet line 5 by a 
pump 6. A suitable strainer 7 can be connected in line 5 to remove solid 
contaminants from the cleaning solution. While the drawing illustrates a 
single strainer being utilized, it is contemplated that a pair of 
strainers may be employed in parallel, with one strainer being utilized 
while the second strainer is down for maintenance or cleaning. 
A concentrated mixture of enzymes and surfactant can be introduced into the 
closed system through line 8, which is connected to line 5, and flow 
through line 8 is controlled by a suitable valve 9. 0n start-up, vessel 1 
may contain only water and the concentrated cleaning solution is then fed 
into the water being circulated through line 5. When the concentration of 
enzymes and surfactant reaches the desired level, the flow through line 8 
can then be terminated. 
The cleaning solution is preferably heated to a temperature in the range of 
about 220.degree. F. to 260.degree. F. and, to achieve this temperature, 
the cleaning solution is passed through line 10 to heat exchanger 11. Flow 
through line 10 can be controlled by valve 12. The heated solution after 
passing through the heat exchanger is conducted through line 13 to line 15 
and flow through line 13 can be controlled by valve 14. In addition, valve 
16 is mounted in line 15 between the junctions of lines 10 and 13. With 
valve 16 closed, and valves 12 and 14 open, the cleaning solution will 
flow through the heat exchanger 11. Conversely, with valves 12 and 14 
closed, and valve 16 open, the cleaning solution will flow directly 
through line 15 to the equipment to be cleaned. 
As illustrated in the drawing, the heating medium used to heat the cleaning 
solution in heat exchanger 11 is steam, which is introduced into the heat 
exchanger through line 17, and valve 18 is mounted in line 17 to control 
the flow therein. Steam condensate is discharged from the heat exchanger 
through line 19. 
Mounted in line 15 is a flow meter 20, which indicates the rate of flow of 
the solution flowing to the equipment to be cleaned. 
Line 5 along with line 15 constitute a supply conduit which is connected to 
one or a series of vessels or other pieces of equipment to be cleaned. As 
shown in the drawing, four closed vessels 22a-22d are connected in series 
and the internal surfaces of the vessels are adapted to be cleaned by 
flowing the cleaning solution through the vessels. While the drawings 
illustrate four vessels 22a-22d being cleaned through the process of the 
invention, it is contemplated that one or more vessels or other pieces of 
equipment may be connected in the closed flow system for cleaning. Line 25 
connects line 15 with the first vessel to be cleaned 22a, while line 26 
connects vessel 22a and 22b, line 27 connects vessel 22b to vessel 22c, 
and line 28 connects vessel 22c to vessel 22d. In addition, line 29 is 
connected to vessel 22d. 
The heated cleaning solution is circulated through vessels 22a-22d at a 
rate generally in the range of 1000 to 3000 gallons per minute. The 
cleaning solution serves to remove oil and lipophilic materials from the 
internal walls of the vessels and also attacks and removes the hydrocarbon 
binders that bonds solid particles of coke or iron sulfide together, thus 
dislodging the particles from the vessel walls. The dislodged particles, 
as well as the oil contaminants, will be flushed from the vessels 22a-22d 
by the flow of the cleaning solution and returned to pressure vessel 1 
through return line 23. 
As a feature of the invention, a reverse flow manifold is incorporated to 
reverse the flow through lines 25 and 29 to provide more effective 
cleaning of the vessels. The reverse flow manifold is particularly useful 
when a series of vessels or other pieces of equipment are connected in 
series for cleaning as shown in the drawing. 
The reverse flow is accomplished by connecting lines 30 and 31 to line 25, 
with line 30 being connected to return line 23 and line 31 being connected 
to line 29. In addition, bypass line 32 connects lines 30 and 29. Valves 
33, 34, 35 and 35a are mounted in lines 30, 29, 32 and 25, respectively. 
With this arrangement, closing valves 33 and 34 and opening valves 35 and 
35a will cause flow through line 25, through vessels 22a-22d, and then 
through line 29 and line 32 to return line 23. On the other hand, closing 
valves 35 and 35a and opening valves 33 and 34, will result in flow in the 
opposite direction through the vessels 22a-22d. 
The cleaning solution being returned through line 23 to pressure vessel 1 
is introduced into the inlet section 3 through a downwardly inclined inlet 
36. The downwardly inclined attitude of inlet 36 will aid in enabling the 
solid particles in the circulating solution to settle in the lower portion 
of vessel 1. 
The invention also includes a provision for periodically discharging or 
purging the solid materials that have collected in the bottom portion of 
inlet section 3 of vessel 1. In this regard, a series of blow-down lines 
37 are connected to the bottom of vessel 1. While the drawings show two 
lines 37, it is contemplated that any number of such lines can be 
utilized, with each line including a flow control valve 38. Lines 37 are 
connected to line 39 which, in turn, is connected to waste storage tank 
40. The closed flow system is normally operating at a pressure in the 
range of about 30 to 60 psig, and by momentarily opening valves 38 in 
lines 37, a blow-down will occur which will cause solid material collected 
in the bottom of pressure vessel 1 to be discharged through lines 37 and 
then to the waste tank 40. 
It is contemplated that suitable strainers can be mounted in lines 37, if 
desired, to strain out the solid particles from the mixture of liquid and 
solid being discharged during the blow-out, so that the solid materials 
will be separated and not be discharged to the waste storage tank 40. 
While the cleaning solution includes a surfactant which would normally tend 
to maintain oil in an emulsified state in the aqueous cleaning solution, 
the combination of enzymes and surfactants has the unusual characteristic 
of enabling the oil to settle out as an oil phase when the cleaning 
solution is maintained in a quiescent state. Thus, the oil which has been 
removed from the vessels 22a-22d and returned to the pressure vessel 1 
with the cleaning solution will settle out in pressure vessel 1 as an 
upper oil phase. This oil phase can be periodically removed through an oil 
drain line 42, which is connected to the pressure vessel at a level in 
alignment with the collected oil phase. This level is slightly above the 
upper edge of weir 2. Line 42 can be connected to line 39 and flow through 
line 42 can be controlled by valve 43. By opening valve 43, the oil can be 
drained from the pressure vessel 1 while the system is operating and the 
oil can then be discharged to the waste storage tank. 
While the drawing shows only a single oil drain line 42 connected to 
pressure vessel 1, it is contemplated that two or more drain lines can be 
used, each connected at a different vertical level to the pressure vessel. 
In addition, suitable sight glasses, not shown, may be connected to vessel 
1 to provide a visual indication of the level of the separated oil layer. 
After determining the level of the oil layer through use of the sight 
glass, the proper oil drain line in the series can be opened to discharge 
the oil. 
When cleaning oil refinery equipment, or other equipment used for 
processing hydrocarbons, benzene may be entrained in the cleaning 
solution. As the cleaning solution is normally operating at a temperature 
above the boiling point of benzene, the benzene will vaporize and the 
vapor will be released from the cleaning solution in pressure vessel 1. 
As shown in the drawings, a perforated tube 44 is mounted in the upper 
portion of pressure vessel 1 in the headspace above the liquid level. Line 
45 is connected to the interior of tube 44 and valve 46 is mounted in line 
45 to control the flow therethrough. Benzene vapor or other hydrocarbon 
gases being released from the circulating cleaning solution in pressure 
vessel 1 will be discharged into tube 44 when valve 46 is open and 
discharged from the vessel through line 45 to a flare or other combustion 
disposal equipment. In order to aid in stripping the gases from the 
cleaning solution, nitrogen gas can be introduced into the lower portion 
of pressure vessel 1. In this regard, a perforated tube 47 is mounted in 
the inlet section 3 adjacent the bottom of the tank and nitrogen is 
introduced into the tube through line 48. Flow through line 48 can be 
controlled by valve 49. The nitrogen will bubble upwardly through the 
cleaning solution to strip the benzene and the gases will then be 
discharged through tube 44 and line 45. 
A conventional pressure regulator valve 50 can be mounted on vessel 1 and 
if the internal pressure exceeds a pre-selected value, valve 50 will open 
to discharge fluid from vessel 1 through line 51 to the waste storage 
tank. 
In operation of the closed system, which normally operates at a pressure of 
30 to 60 psig, the cleaning solution will be continuously circulated from 
the pressure vessel 1 by pump 6, through the heat exchanger 11, and then 
through the vessel 22a-22d to be cleaned, and then returned through line 
23 to the pressure vessel. Periodically the flow through the vessels 
22a-22d can be reversed to provide more effective cleaning and flushing of 
the dislodged particles. 
As the system is pressurized and is not open to the atmosphere, 
temperatures above the boiling point of water can be employed without 
foaming of the cleaning solution. This is important since the cleaning 
solution contains a major concentration of a surfactant which promotes 
foaming. 
The system of the invention enables oil and solid material to be 
periodically removed from pressure vessel 1 while the cleaning operation 
is in process. The process also removes hydrocarbon gases, such as 
benzene, from the pressure vessel for suitable disposal or combustion, so 
that there is no release of any components to the atmosphere. 
Various modes of carrying out the invention are contemplated as being 
within the scope of the following claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the invention.