Abstract:
Vacuum trucks are utilized for collecting liquids and solids capable of fluidization, via a hose or pipe connected to a holding tank in which a vacuum has been induced via an air mover such as a blower. The air stream drawn from the holding tank must be discharged to the atmosphere; environmental laws may require treatment of the exhaust stream prior to discharge. Vacuum trucks used in industrial settings like petroleum refineries and chemical plants may require a large charge of materials to remove pollutants discharged from the vacuum truck holding tank. The embodiments disclosed herein include modularized “control units,” containing adsorbents and/or absorbents to reduce the organic content of the exhaust gas, including VOCs as well as specific organic compounds of concern. These materials must be replaced when they are no longer effective in removing pollutants. Embodiments herein include a system for efficient change out of control units to allow continued operation. This apparatus and method allows for the change out of the control units at the location or site of the operation of the vacuum unit rather than requiring return to a service point.

Description:
[0001]    Embodiments disclosed herein may be used for to control organic pollutants in an exhaust stream from the holding tank of a vacuum truck. Vacuum trucks are utilized for collecting liquids and solids capable of fluidization, via a hose or pipe connected to a holding tank in which a vacuum has been induced via an air mover such as a blower. The air stream drawn from the holding tank must be discharged to the atmosphere; environmental laws may require treatment of the exhaust stream prior to discharge. Many times the collected liquid is organic in nature or contains organic materials. Of concern is a general class of volatile organic compounds (VOCs) and specific compounds such as benzene. The embodiments disclosed herein include modularized “control units,” containing adsorbents and/or absorbents to reduce the organic content of the exhaust gas, including VOCs as well as specific organic compounds of concern. 
         [0002]    It is well known that low vapor pressure organic liquids (like diesel) and activated carbon are effective at reducing the organic content of a vent gas. Ultimately, absorbents and adsorbents become saturated with organic contaminants and must be replaced. Embodiments herein include a system for efficient change out of control units to allow continued operation. This apparatus and method allows for the change out of the control units at the location or site of the operation of the vacuum unit rather than requiring return to a service point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  shows a simplified block flow diagram of a vacuum truck. 
           [0004]      FIG. 2  shows a flow diagram of the VOC pollution control device. 
           [0005]      FIG. 3  shows a partial cross-sectional side view of a single control unit. 
           [0006]      FIG. 4  shows a side view of the control panel. 
       
    
    
     DETAILED DESCRIPTION 
     Parts List 
       [0000]    
       
         Holding tank  100   
         Holding tank suction line  110   
         Draining canister  120   
         Draining canister valve  125   
         Drained liquid stream  128   
         Vacuum pump  130   
         Draining canister  140   
         Draining canister valve  145   
         Drained liquid stream  148   
         VOC pollution control device  150   
         Final canister  160   
         Holding tank exhaust  200   
         Vacuum pump suction  210   
         Control device inlet  220   
         Treated exhaust stream  230   
         Inlet split to Control unit 1  300   
         Control unit 1 inlet valve  310   
         Control unit 1 inlet line  320   
         Inlet 1 flexible hose  330   
         Outlet 1 flexible hose  340   
         Outlet 1 Hard pipe  350   
         Control unit 1 outlet  360   
         Control unit 1 outlet valve  370   
         Secondary inlet  380   
         Inlet split to Control unit 2  400   
         Control unit 2 inlet valve  410   
         Control unit 2 inlet line  420   
         Inlet 2 flexible hose  430   
         Outlet 2 flexible hose  440   
         Outlet 2 Hard pipe  450   
         Control unit 2 outlet  460   
         Control unit 2 outlet valve  470   
         Secondary inlet  480   
         Discharge valve 1  500   
         Discharge valve 2  510   
         Control device outlet  520   
         Control panel  600   
         Top transport valve  610   
         Engine Shut off switch  620   
         Bypass control unit switch  630   
         Bypass control unit indicator  635   
         Control unit system switch  640   
         Control unit 1 primary indicator  643   
         Control unit 2 primary indicator  648   
         Rear works light switch  650   
         Power switch  660   
         Power indicator  670   
         Hose 1 inlet connector  700   
         Hose 1 outlet connector  710   
         Hose 2 inlet connector  720   
         Hose 2 outlet connector  730   
         Hose 3 inlet connector  740   
         Hose 3 outlet connector  750   
         Hose 4 inlet connector  760   
         Hose 4 outlet connector  770   
         Control unit No. 1  801   
         Control unit No. 2  802   
         Control unit 1 vapor in line  811   
         Control unit 2 vapor in line  812   
         Control unit diffuser line  820   
         Control unit screen support  830   
         Lower Control unit screen  840   
         Upper hold down screen  845   
         Control unit liquid drain  850   
         Control unit liquid  860   
         Control unit carbon  870   
         Control unit outlet screen  880   
         Control unit 1 vapor outlet line  891   
         Control unit 2 vapor outlet line  892   
         Control unit base  900   
         Control unit base forklift inlets  910   
       
     
         [0078]    Reference is made to  FIG. 1  which contains a simple schematic flow diagram of a typical vacuum truck with a control device for the exhaust stream. The purpose of the system is to draw a liquid into the holding tank  100  through a hose or pipe, connected to the holding tank suction line  110 . Liquid is induced into the holding tank  100  which is under a vacuum. A vacuum is created in the holding tank  100  by an air mover, blower, or vacuum pump  130  that pulls a stream of air out of the holding tank  100 , referred herein as the holding tank exhaust  200 . The exhaust stream  200  is routed through a control device  150  and ultimately a treated exhaust stream  230  is discharged to the atmosphere. 
         [0079]    The embodiment shown in  FIG. 1  contains optional canisters or filters to remove entrained liquids or solids from the exhaust streams. The canisters may be filled with a high surface area material such as a filter material or packing material, or may utilize tangential forces to separate liquids and solids from the exhaust stream. Other means that facilitate separation of liquid and solid material from the exhaust stream may also be used. A draining canister  120  is located upstream of the vacuum pump  130 , to provide protection from entrained liquids and solids. The upstream draining canister  120  is equipped with a draining canister valve  125  to facilitate removal of the drained liquid stream  128 . An optional draining canister  140  is located downstream of the vacuum pump  130  and is equipped with a draining canister valve  145  to facilitate removal of the drained liquid stream  148 . A final canister  160  is located downstream of the control device  150  prior to discharge of the treated exhaust stream  230 . 
         [0080]    The embodiment presented in  FIG. 1  shows the holding tank  100  and control devices  150  attached to a mobile platform that in this example is the flatbed of truck. In other embodiments, some or all of the equipment may be attached to different mobile platforms, such as a skid-mounted deck, capable of transportation. 
         [0081]    Referring now to  FIG. 2  which shows the VOC pollution control device  150  in greater detail. In the embodiment shown in  FIG. 2 , the pollution control device  150  contains two control units  801  and  802 . The control units contain adsorbent and/or adsorbent media capable of capturing VOCs and specific organic molecules of concern. Although this embodiment presents two control units, the pollution control device  150  may have one or more control units. The number of control units is limited by the pressure drop through the control units at the desired flow rate. As presented in  FIG. 2 , this embodiment has a valve arrangement that allows for parallel or series flow through control unit no. 1  801  and control unit no. 2  802 . Parallel flow may be initiated by opening control unit 1 inlet valve  310 , control unit 2 inlet valve  410 , discharge valve 1  500 , and discharge valve 2  510 , while closing control unit 1 outlet valve  370  and control unit 2 outlet valve  470 . 
         [0082]    Conversely, the control units can operate in series by coordinating the position of the valve (open or closed) according to groups. Group one would include control unit 1 inlet valve  310 , control unit 1 outlet valve  370 , and discharge valve 1  500 . Group two would include control unit 2 inlet valve  410 , control unit 2 outlet valve  470 , and discharge valve 2  510 . Operation of this embodiment in series flow occurs by operating Group one valve in the opposite position from Group two valves. Operation of the Group one valves in the open position (and thus Group two in the closed position) results in control unit no. 1  801  being the primary control unit (i.e., first control unit the series) and control unit no. 2  802  being the secondary control unit (i.e., receives flow from the primary control unit). The order of flow can be changed by reversing the valve positions by closing Group one valves and opening Group two valve. Under this circumstance, control unit no. 2  802  becomes primary and control unit no 1  801  becomes secondary. 
         [0083]    Considering  FIG. 2  further, flow enters the VOC pollution control device  150  at the control device inlet  220 . This line divides so as to allow either series or parallel flow as described previously. One branch is referred to as the inlet split to control unit 1  300  and the other split is referred to as inlet spilt to control unit 2  400 . Considering series flow where Group one valves are in the open position, flow or holding tank exhaust  200  is routed to control unit no. 1  801  via control unit inlet valve  310  to control unit 1 inlet line  320 ; control unit 2 outlet valve  470  is closed. 
         [0084]    An important feature of the embodiment shown in  FIG. 2  is a piping system configuration that facilitates the “change-out” of a spent control unit. At some point, each the absorbent and/or adsorbent material in the control unit will no longer remove pollutants effectively and will require replacement. Under typical operations, the primary control unit becomes spent first, having the highest loading of organic contaminants, and must be replaced. After the spent control unit is replaced, the truck operator should switch the groups so that the new control unit (now located in the position of the replaced and former primary control unit) becomes the secondary control unit and the (former) secondary control unit becomes the (post-switch) primary control unit. 
         [0085]    Continuing with the series flow example, the holding tank exhaust  200  is routed from the control unit inlet line  320  to the inlet 1 flexible hose  330 . This hose is connected to the control unit 1 inlet line  320  via the hose 1 inlet connector  700 . The outlet of the inlet 1 flexible hose  330  is connected to the control unit 1 vapor in line  811  via the hose 1 outlet connector  710 . In this embodiment, vapor enters the bottom of the control unit and exists at the top via the control unit 1 vapor outlet line  891 . This line is attached to outlet 1 flexible pipe  340 , which is routed via a series of lines shown as the outlet 1 hard pipe  350 , control unit no 1 outlet  360  through an open control unit no. 1 outlet valve  370  to the secondary inlet  380 ; in this example, discharge valve 2  510  is closed. The control unit inlet valve  410  is shut, forcing flow through control unit no. 2  802  (which in this example is a secondary control unit). Flow proceeds through control unit no. 2  802  through the control unit 2 inlet line  420 , through the inlet 2 flexible hose  430 , entering the bottom and exiting the top of control unit no. 2  802 , passing through the outlet 2 flexible hose  440  to the outlet 2 hard pipe to discharge valve no. 1  500  (given that control unit 2 outlet valve  470  and discharge valve 2  510  are closed). Flow from the pollution control device  150  exits via the control device outlet  520 . 
         [0086]    While the above description illustrates one configuration of how the function of two control units may be coordinated; other combinations may allow for the same function, and in many instances specific pieces of pipe could be eliminated, simplifying the system. For example, outlet 1 flexible hose could be coupled directly to control unit 1 outlet  360  without first passing through outlet 1 hard pipe  350 . In all cases hard pipes may be substituted with flexible pipe/hoses and vice versa. Configuration with a single control unit would be significantly simplified and configurations with more than two control units would become more involved. 
         [0087]    Reference is now made to  FIG. 3  which shows a control unit in greater detail. Control units may be identically configured or may be differently configured. In this example, control unit no. 1  801  and control unit no. 2  802  are similarly configured. Vapor enters the control unit via an internal control unit diffuser line  820 . The control unit contains an absorbent liquid designated as control unit liquid  860 . A purpose of the liquid is to capture entrained or condensed liquids prior to proceeding to the control unit carbon  870  (which is supported by the control unit screen support  830  and the lower control unit screen  840  and optionally retained by an upper hold down screen  845 ), so as to prolong the useful life of the carbon bed. 
         [0088]    Proper selection of the nature and composition of the control unit liquid  860  is dependent on the nature of the material being recovered by the vacuum truck. A simple low vapor pressure organic mixture, such as diesel, is appropriate where recovering an organic material, or another material that contains organic contaminants. Other organic liquids may be used for the same purpose. In another example, the control unit liquid  860  may be or contain a surfactant or degassing chemical. In another example, the control unit liquid  860  may be a caustic solution or another chemical capable of removing inorganic substances such as hydrogen sulfide. In yet another example, the control unit liquid  860  could be an aqueous solution, adjusted to a desired pH, with or without addition of surfactants. Ultimately, the purpose of the control unit liquid is the removal of contaminants that shorten the life of the carbon bed. 
         [0089]    Vapor, after passing through the control unit liquid  860  and the control unit carbon  870 , exits the control unit via the vapor outlet line, being  891  for the control unit 1 outlet vapor line and  892  for the control unit 2 vapor outlet line. The vapor outlet line may be equipped with a control unit outlet screen  880  to hold back solid material (such as carbon). Control units may be configured as described above with a control unit liquid  860  and carbon  870 , or alternatively with control unit liquid  860  only, or carbon  870  only. 
         [0090]    Reference is now made to  FIG. 4  which shows the control panel. Although the system of valves discussed previously could be operated manually, one embodiment includes a control system to coordinate the valves and monitor the operation of the system. In this embodiment, power is enabled to the control system via power switch  660  and indicated by power indicator  670 . The rear lights work light switch  650  activates the rear working lights. The control unit system switch  640  coordinates the valve groups so a designate which control unit is primary and which is secondary. In this embodiment, control unit no. 1  801  is the primary control unit when the control unit 1 primary indicator  643  is activated. Likewise, control unit no. 2  802  is the primary control unit when the control unit 2 primary indicator  648  is activated. In this embodiment, the control system also allows complete bypass of the pollution control device  150  via the bypass control unit switch  630  as indicated by the bypass control unit indicator  635 . The control panel in this embodiment has a switch to close the top transport valve  610  and an emergency engine shut-off  620 . The top transport valve  610  should be secured prior to transporting a vacuum truck containing a load of received liquid. The emergency shut off  620  is used to shut of air from the engine in an emergency. 
         [0091]    One embodiment of the apparatus described herein is configured with at least two control units. The exhaust stream leaving the tank is initially routed to the (primary) control unit that is closest to being spent. The partially treated steam exits the initial control unit and is routed to the inlet of the “fresher” (secondary) control unit. The secondary control unit is fresher because it has adsorbed and/or absorbed less organic material. At some point in time, the primary control unit, having practically exhausted its adsorption and/or adsorption capacity, becomes spent and must be replaced. 
         [0092]    Vacuum trucks with VOC pollution control devices already exist. See U.S. Pat. No. 7,147,689 (filed Apr. 30, 2004) (issued Dec. 12, 2006). Embodiments disclosed herein have similarities to these inventions as both allow for operation of the vacuum truck with reduced emissions of VOCs. Effective control systems, designed to remove VOCs based on absorption with organic liquids or adsorption with activated carbon, have inherent limitations. “Break-through” of the organic vapors occurs when the holding capacity of the oil and/or carbon reaches a certain level. Where an emission limit is reached, upon beak-through, it is necessary for the vacuum truck to stop operation and return to servicing point (often offsite) for a fresh charge of adsorbent and/or absorbent. 
         [0093]    Efficient utilization of vacuum trucks, where requirements for a high degree of VOC removal is required, requires relative large charges of VOC adsorption and/or absorption materials to operate for significant periods of time. For a given load of adsorbent/absorbent, the time of satisfactory operation is dependent on the nature and content of the organic vapors being treated and the required discharge quality. It is often desirable that the control units have sufficient capacity to meet objective criteria for a minimum of an eight to twelve hour shift. Control units installed on vacuum trucks in industrial (e.g., petroleum or chemical facility) service may be substantial in size in order to meet environmental requirements. In one embodiment, a fully charge control unit may contain both a thousand or more pounds of carbon and another thousand or more pounds of liquid. Such control units require mechanical means for replacement. 
         [0094]    One method of servicing the vacuum truck VOC control system would be to return to a central servicing point where the adsorption/absorption material is removed and replaced with fresh material. Such requires travel to the central servicing location resulting in a loss of operating time due to the unavailability of the vacuum truck. Availability of a systematic, modularized, and quick method of changing control units, at the location of the vacuum truck&#39;s operation would significantly reduce downtime and unavailability of vacuum trucks. Embodiments herein include a system for efficient change out of control units to allow continued operation at the location or site of the required work. 
         [0095]    At times, it is necessary to operate a multistage system to meet environmental requirements. In a two stage system, after use for a period of time, the second stage (also known as the secondary stage) may have insufficient adsorption/absorption capacity to “polish off” the final discharge to meet discharge concentration/mass limitations; however it may have sufficient capacity remaining to act as the primary control unit. Embodiments contain herein allow for switching of control units from secondary to primary, while adding a fresh control unit (in place of the formally spent primary control unit) that is inserted in the pollution control device  150  to be the “new” secondary control unit. Such allows for maximum utilization of adsorption/absorption material prior to removal/disposal. The inability of systems to efficiently and quickly replace only the spent control unit adds to inefficiency in the system. When it is necessary to move the vacuum truck to an off-site location, overriding time constraints could cause the operator to dump and replace both the primary and secondary control unit, even though the secondary control unit may have some useful life, to minimize future downtime, resulting in an incomplete use of the media in the secondary control unit. 
         [0096]    Configured as previously described, the apparatus and methods described herein facilitate the quick switching of individual control units. Prior to switching out the spent control unit for a fresh control unit, the system should be powered down by switching-off power to the system, in this embodiment via power switch  660 . After preparation efforts, the first step in the quick switch control unit change out procedure (i.e., replacing the spent control unit) is to switch the primary control unit flow by switching the valve arrangement via the control unit system switch  640  such that the holding tank exhaust stream  200  is moved from the inlet of the spent control unit to the inlet of the other, fresher control unit. After switch the positions of the valves, the (former) secondary control unit become the (post-switch) primary control unit. 
         [0097]    The second step in the quick switch control unit change out procedure is to physically disconnect the spent control unit from the connection to the mobile platform (such as the flatbed of the truck). As shown in  FIG. 3 , each control unit has a control unit base  900 . This base is attached to the mobile platform in a secure, yet easy to release manner. In this embodiment, two rectangular metal strips are permanently attached in the vertical position or perpendicular to the mobile platform to position and secure the control unit base  900 . These two metal strips are parallel to each other and separated by a distance just greater than the horizontal distance of the control unit base  900 . The two parallel metal strips are at least as tall as the vertical height of the control unit base  900  and may have a horizontal plate attached to the highest part of the metal strip to function as a hold-down plate. This hold-down plate is parallel to the mobile platform and perpendicular to the metal strip. The control unit base is further secured via a latch that is secured to the mobile platform and either bolts directly to the control unit base  900 , or reaches across the control unit base and attaches to another location on the mobile platform. As described in the above example, the means of attachment between the control unit and the mobile platform is temporary yet secure. 
         [0098]    The third step in the quick switch control unit change out procedure is to disconnect the vapor inlet and vapor outlet hoses connections, shown in  FIG. 2  as connections  710  and  720 , or  750  and  760 , depending on whether control unit no. 1  801  or control unit no. 2  802  is being removed. After the control unit base  900  and associated hoses have been disconnected, the spent control unit may be removed from the flatbed of the vacuum truck. 
         [0099]    The fourth step in the quick switch control unit change out procedure is to remove the spent control unit. In this embodiment, as shown in  FIG. 3 , the spent control unit is equipped with forklift inlets  910  in the base  900  so as to facilitate removal from the vacuum truck flatbed via a fork lift. Other methods of removing the spent control unit may be used such as configuring the control unit with secure fixtures to facilitate removal with a lifting line. 
         [0100]    The fifth step in the quick switch control unit change out procedure is to install a clean control unit in the place of the spent (and now removed) control unit. The new control unit is put in place by actions reverse to methods described previously for removal of the spent control unit. After being placed in the location previously held by the spent control unit, the base  900  of the fresh control unit is secured to the flatbed of the vacuum truck as described previously. 
         [0101]    The sixth step in the quick switch control unit change out procedure is to reconnect the vapor-in and vapor-out hose connections. At this point, the spent control unit has been removed and replaced with a new control unit. Since the primary control unit flow was reversed in step one, the fresh control unit is secondary and the remaining control unit is now primary. The system is now ready for activation.