Abstract:
The invention relates to a compressed air foam producer, wherein a fire or decontamination specific additive is injected directly into the foam forming flow supplied to the main water flow and/or the main water flow. A mixing pump for the foaming agent draws off an auxiliary and motive water flow, wherein initially the additive and then the foaming agent is injected. The foaming agent-additive-water mixture, which is produced directly on site, is mixed well together and with the main water flow ensuring a fine, uniform distribution of the additives in the compressed air foam. The thus produced compressed air foam ensures optimal, economical and environmentally friendly fire-fighting and decontamination.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method of producing compressed air foam (CAF) for fire fighting and decontamination in which a main water stream is mixed with a foaming agent stream and the mixture of water and foaming agent is foamed along a foaming line with a compressed air stream, and further relates to an arrangement for performing the method. 
     2. Description of Related Art 
     The generation of CAF alone in the way described above is known. When this document mentions CAF production with compressed air, the term ‘compressed air’ is of course meant to include pressurized gases suitable for fire extinction. Fire fighting and decontamination of objects with CAF has proved its worth in many application cases. Formulated application-specific mixtures of foaming agents and specific additives are provided to be able to use the CAF as optimally and efficiently as possible for the respective type of fire or contamination with as little environmental impact as possible. The production and provision of such mixtures is limited inasmuch as foaming agents with specific additives adjusted to the respective type of fire or decontamination often dissolve with difficulty or not at all in the stock solution, result in high-viscosity mixtures or tend to clot, which makes them hard to deliver or distribute evenly their full effect. Apart from difficulties in the production or provision and processing of mixtures with the most varied additives, it is also not feasible to keep a multitude of mixtures or even a mixture of the same components in different compositions available at the respective set and for the respective application case, for example to enable optimum fire fighting using variable portions of additives. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to state a method of producing compressed air foam (CAF) that ensures high efficiency in terms of its effectiveness, quantity of agents used, and environmental impact in different applications and conditions of use depending on the type of the fire or decontamination as well as a plant for performing this method with as little hardware use as possible. 
     This problem is solved according to the invention by the method and apparatus disclosed herein. 
     The inventive idea, in other words, is that during the production of the CAF, i.e. directly on the application site, at least one specific additive adjusted to the respective type of fire or the respective decontamination purpose is admixed to a stream of foaming agent that is added to the main water stream or directly to the main water stream and ensures an optimum effect of the CAF with regard to fast and safe fire fighting or decontamination. It was found that the addition of just one special additive is sufficient and that it is especially the accurately dosed separate feeding of the additive into the foaming agent stream that ensures thorough mixing in the foaming agent and particularly a uniform, fine distribution in the fire extinguishing or decontamination foam resulting in maximum effectiveness of the additive combined with low consumption and reduced environmental pollution. In particular, various types of fires and various and differently contaminated objects can be fought or decontaminated effectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a system for producing a two-component foam in two foaming lines having different foaming capacities; and 
         FIG. 2  is a representation of a programmable logic controller with digital and analog electric inputs and outputs. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a preferred improvement of the method according to the invention, the additive is first injected into an auxiliary and motive water stream by aspirating the respective additive based on the water jet pump principle while an auxiliary and motive water stream for the fire extinguishing or decontaminating agent is produced by suctioning off the main water stream using the same admixing pump that also aspirates the foaming agent from a tank for foaming agent. The introduction of the additive and the foaming agent into a water jet already provides good premixing and finally ensures even distribution in the main water stream. 
     In another embodiment of the invention, foaming agent and additive are admixed at different mixing ratios depending on a pressure and water volume control system of the auxiliary and motive water stream in conjunction with the adjustable admixing pump speed. It is of course possible to just introduce the foaming agent or the respective additive or none of the two into the main water stream. 
     In an embodiment of the method, the auxiliary or motive water stream can be used to introduce an antifreeze or rinsing agent instead of an additive into the system. 
     In another embodiment, the foam pressure and thus the quality of the CAF produced with the additive and the foaming agent can be influenced by modifying the foaming period using a valve arrangement. 
     The arrangement according to the invention for performing the method, for the case where an additive is admixed to the foaming agent, includes a mixer that is integrated into the main water stream in which the main water stream is intermixed with the additive-water-foaming agent mixture. An additive container that is in a functional connection with the admixing pump is provided for intermixing the foaming agent aspirated with the admixing pump and the respective additive. The admixing pump is connected to the main water stream to provide the auxiliary and motive water stream via a bypass line to which first a Venturi admixer and then the foaming agent tank are connected in the direction of flow. The admixing pump is preferably driven by a pneumatic motor that takes the required driving air from the main air stream for compressed air foaming and can be controlled using an air pressure and air volume controller. A speed-controlled DC motor to which the zero shift of non-stall-resistant motors described below can be applied and can be used instead of the pneumatic motor. A pressure sensor is associated with an upstream water pressure controller and a downstream water volume flowrate control unit are connected to the Venturi admixer. The required quantities of foaming agent and additive can be set by a controller using the respective pressure conditions and volume flowrates. The mixer is provided with two injection nozzles with different k values to introduce differing quantities of foaming agent-additive mixture into the main water stream. 
     The arrangement according to the invention can be used to provide compressed air foams using the method described above that contain an additive admixed in situ at different quantities depending on the respective application case, i.e. the type of fire or decontamination, and evenly distributed in the foam so that these foams enable efficient fire fighting and decontamination. The system is of a very simple design as it uses compressed air and water as energy sources for operating the admixing system which are required anyway for producing the CAF. While the foaming agents are generally the same, all that is needed to be held in stock are different additives that are finely and evenly admixed into, and distributed in, the foaming agent without demixing or clotting and contained in the same even distribution in the fire extinguishing or decontaminating foam so that they can unfold their full effect. 
     One embodiment of the invention is explained in more detail with reference to  FIG. 1  that shows the schematic diagram of a system for producing a two-component foam in two foaming lines having different foaming capacities. 
     A programmable logic controller  1  with digital and analog electric inputs and outputs that cooperates with the system-specific sensors and control valves is assigned to the system for monitoring and control. The arrows A, B, C, and D represent the main water stream, the main airstream, the auxiliary and motive water stream, and the drive air stream, respectively. 
     Water is fed into the system from a fire extinguishing pump or pressurized-water reservoir (not shown) and flows via a water filter  2 , a water pressure controller  3 , a water volume flowrate control unit  4 , and a water pressure sensor  5  into a mixer  6 . Two injection nozzles  7  with different k values lead into the mixer  6  via which injection nozzles  7  a mixture of a commercial foaming agent (SB) and an application-specific second component (Add) depending on the current fire fighting or decontaminating requirements is fed into the water volume flow. The water volume flow intermixed with the two components (foaming agent and additive) flows via first and second water flowrate control valves  8  or  9 , respectively, into a first or second foaming line  10  and  11  in which the respective water mixture is foamed using compressed air. The first or second, respectively, compressed air foam produced in this way flows via foam pressure sensors  12  or  13  and electro-pneumatically operated valves  14 ,  15  or  16 ,  17 , respectively, that form a closed-loop control circuit for setting the foam consistency and consequently, the foam quality to the respective foam ejection device (not shown). Compressed air is conducted into the foaming lines  10 ,  11  from a compressed air source or a compressor (not shown) via an air filter  18 , an air pressure controller  19 , an air pressure sensor  20  and respective first and second air volume flowrate control valves  21  located upstream of respective the foaming lines  10 ,  11 . 
     As mentioned above, a foaming agent and an additive adjusted to the respective application case with which the fire can be fought in a controlled manner and more efficiently than before are injected into the water volume flow using the mixer  6 . The substances are admixed from a foaming agent tank  23  and an additive container  24  that was filled before use with an additive that is adjusted to the type of fire or substances to be decontaminated and highly effective but cannot be mixed durably and homogeneously with the foaming agent. The foaming agent tank  23  and the additive container  24  are connected to a bypass line  25  that branches off from the overall water flow downstream of the water filter  2  and runs into the injection nozzles  7  of the mixer  6  at its other end. An admixing pump  26  with upstream water pressure controller  27 , a Venturi admixer  28  and a water flowrate control unit  29  is inserted into the bypass line  25 . The additive container  24  is connected to the Venturi admixer  28  via a valve  30 , and a delivery line from the foaming agent tank  23  runs directly into the bypass line  25  upstream of the admixing pump  26 . A valve  31  for flushing and bleeding the admixing pump  26  and a flow meter  32  are integrated into the portion of the bypass line  25  that is located between the mixer  6  and the admixing pump  26 . The admixing pump  26  is driven by a pneumatic motor  33  that is connected to the compressed air feed line behind the air filter  18  via an air pressure controller  34  for setting the operating pressure and an air volume flowrate control valve  35  for controlling the motor speed. 
     The foaming agent with additive fed via the bypass line  25  is injected into the water volume flow delivered by the mixer  6 . The foaming agent-additive-water mixture flows via the water volume flowrate control valves  8  and/or  9  and the compressed air foam generators  10  and/or  11  into which compressed air is inserted at preset pressure and volume parameters via the air volume flowrate control valves  21  and/or  22 . The foam quality of the compressed air foam spread using foam ejecting devices (not shown) depends on the flow rate and therefore on the dwell time of the foam in the foaming lines  10 ,  11  and is controlled via the foam pressure determined by the foam pressure sensors  12 ,  13  using valves  14 ,  15  or  16 ,  17 , respectively (foam pressure control). 
     The speed of the pneumatic motor  33  of the admixing pump  26  is controlled by the air volume flowrate control valve  35 . The controller  1  determines the setpoint control signal for the motor speed in conjunction with the pump characteristic from the setpoint value preset for the foaming agent-additive admixing rate and the actual value determined by the water volume flow sensor  4 . In the embodiment shown here—without using a flow meter for the foaming agent—the pressure difference between the initial pressure at the admixing pump  26  and the flow pressure of the water at the inlet of the mixer  6  is measured using the water pressure sensor  5  and the pressure sensor  32 . The foaming agent-additive mixture is injected into the water stream via the injection nozzles  7 . The volume flows through the respective injection nozzle  7  as a function of the differential pressure are stored as a parameter table in the controller  1 . The admixture of foaming agent and additive is controlled depending on pressure using the setpoint values preset in comparison with the water volume flow determined by the water flow sensor  4 , the speed control of the admixing pump  26 , the differential pressure measurement mentioned above, and the parameter tables stored in the controller  1 . To ensure as small pressure-volume flow curves as possible, smaller volume flows or volume flows defined in specific limits are admixed using an injection nozzle  7  with a small k value while a second injection nozzle  7  with a larger k value is connected via the valve  36  for larger volume flows, thereby ensuring a maximum volume flow for admixing the foaming agent-additive mixture. 
     According to the embodiment discussed here, volume flowrate control valves  8 ,  9  for the water-foaming agent-additive mixture and air volume flowrate control valves  21 ,  22  are inserted upstream of the respective CAF generator  10 ,  11  to be able to provide even very small volume flows, especially when decontaminating. 
     The foaming agent and the other specific component depending on the respective type of fire or decontamination job are admixed using the admixing pump  26  which is driven by a pneumatic motor  33  speed-controllable to adjust capacity using the air volume flowrate control valve  35 . Water is aspirated through the bypass line connected to the main water stream via the water pressure controller  27  and the Venturi mixer as well as the water volume flowrate control unit  29  using the admixing pump  26 . 
     As the pneumatic motors, mostly designed as compressed air rotating piston type motors, are not stall-resistant at a specific speed, i.e. stall at slow speeds and high torques, which means that major mechanical damage is prevented in case of failure but that the admixing pumps cannot continuously be driven from standstill to maximum speed, a defined water volume flow of a size which the admixing pump  26  would deliver at the stalling torque or stalling speed of the pneumatic motor  33  is injected into the bypass line on the inlet side of the admixing pump  26  via the water pressure controller  27  and the water volume flowrate control unit  29 . The admixing pump  26  must rotate at stalling speed for the injected water volume flow to flow. When the speed is increased, foaming agent is aspirated from the foaming agent tank  23  at the desired quantity (between zero and a maximum) in proportion to the speed due to the limited water volume flow injected. The injected water volume flow prevents the admixing pump from running dry and supports the aspiration process when aspirating the foaming agent. If no additive is to be aspirated as fire- or decontamination-specific component, the auxiliary water flow can be shut down by closing the water volume flowrate control unit  29 , and the entire capacity of the admixing pump  26  can be used for delivering foaming agent. The zero shift caused with the arrangement described above of the non-stall-resistant pneumatic motor  33  can similarly be used for speed-controlled DC motors applied instead of the pneumatic motor. 
     The second component that is—if necessary—to be admixed to the foaming agent is aspirated, with the valve  30  open, from the additive container  24  in proportion to the differential pressure via the auxiliary water stream mentioned above that flows through the Venturi admixer  28  at a pressure set by the water pressure controller  27  and while reducing the differential pressure using the water volume flowrate control unit  29  and intensely intermixed with the auxiliary water stream if the speed of the admixing pump  26  is increased using the air volume flowrate control unit at the same time. At increased pump speed and simultaneously constant differential pressure, the admixing pump  26  aspirates foaming agent from the foaming agent tank  23  via the Venturi admixer  28  together with the auxiliary water stream and the additive while both partial streams are intensely intermixed. 
     Thus an additive suitable for the specific application case can be added to the main water stream together with a foaming agent in the mixer  6  enabling highly controlled and effective fire fighting or decontamination. The foaming agent and the additive may be mixed at variable ratios in the quantities required. The foaming agent and the additive can also be the sole admixed substances: the foaming agent can be admixed solely in quantities from zero to a maximum related to the delivery volume of the admixing pump  26 , the additive up to the 1.6-fold of the auxiliary and motive water stream flowing through the Venturi admixer  28 .