Patent Publication Number: US-2011052421-A1

Title: Method and device for controlling the condenser cooling water of a steam-jet vacuum pump

Description:
Up to now, the level of the condenser cooling water in condensers of steam-jet vacuum pumps in non-barometric installation is not controlled. Usually, pumps are used which run with a fixed setting and the delivery volume of which is dimensioned with great inaccuracy for the duty point of the system. Thus, the cooling water level is always within a range limited by alarm and level switches mounted within the condenser. 
     Before a steam-jet vacuum pump can be started, the so-called condenser cooling water circuit has to be started and has to run in a stable manner. 
     The start of the condenser cooling water in the condensers is carried out under atmospheric conditions. 
     As soon as the steam-jet air ejectors are connected, potentially in combination with water ring pumps, and a subsequent vacuum is generated, the negative pressure in the condensers changes. Simultaneously with this change of the negative pressure in the condensers, the differential pressure at the condenser cooling water nozzles, through which the cooling water is fed into the condenser interior, changes. However, with the change of the differential pressure at the nozzles, the water flow rate through the nozzles changes as well which means that with increasing negative pressure, the water flow rate increases as well. 
     This water supply into the condensers, which is higher depending on the respective vacuum, has to be pumped out by the condenser cooling water pumps. To be able to manage the different occurring water quantities to some degree, from case to case, two pumps with different delivery characteristics for large and small quantities of water are used; however, in many cases, this not implemented for cost reasons. 
     To be able to manage the water quantities to some degree, which water quantities are different depending on the operating state of the steam-jet vacuum pump, the energy-inefficient custom has developed to throttle the pumps on the pressure side by means of balancing dampers. At the same time, by using adjusted pipe constructions and isometrics, and further by mechanical valves, attempts have been made not exceed a maximum inflow pressure to prevent that the condensers are flooded which could result in a collapse of the vacuum. 
     However, this can be counteracted by a higher suction flow of the pumps. On the other hand, when the incoming water quantity is too small, a suction flow of the pumps that is too high results in cavitation and thus in increased susceptibility to failure of the pump. 
     Substantially, with the previously common operation mode, the different water quantities occurring in the condensers are difficult to manage and there are recurring undefined states which can build-up until the generated vacuum breaks down. 
     Principally, this unsatisfactory state could be improved by using a speed-controlled pump; however, for this, the cooling water quantities involved in each case must be known. A measurement within the condenser interior is excluded due to the turbulences existing therein and the large amounts of spray. 
    
    
     This unsatisfactory state can be resolved in a surprisingly simple manner by an operation mode according to the present invention. 
     According to this, the level of the cooling water in the condensers ( 1 ,  2 ) is measured in a measuring pot ( 9 ), which is configured as communicating container and which is arranged outside of the condenser, by means of measuring method suitable for vacuum operation such as, for example, a radar or a laser probe ( 10 ), and this measured value is used as signal and controlled variable for a speed-controlled cooling water pump ( 8 ). 
     The device for carrying out the above described method consists, according to the invention, of measuring pot ( 9 ) which is arranged outside of the condensers ( 1 ,  2 ) and which is configured as communicating container, wherein the measuring pot has a pressure equalization line which ensures that the same negative pressure is provided in the condenser interior and the measuring pot ( 9 ), and a measuring probe ( 10 ) for level measuring which is mounted to the upper closure cover and which is suitable for vacuum operation, wherein the measured value of the measuring probe provides the input signal for controlling the speed-controlled cooling water pumps ( 8 ). For safety reasons, an additional mechanical float switch ( 12 ) is mounted inside the level measuring pot ( 9 ), by means of which float switch an alarm cutoff is triggered in the event of a level that rises too high. 
     The connection line ( 13 ) to the condensers&#39; ( 1 ,  2 ) down pipes ( 4 ), by means of which the level within the measuring pot ( 9 ) is leveled, is arranged at the lower end of the measuring pot ( 9 ) and is arranged in such a manner that it extends away from the lower end of the measuring pot ( 9 ) at an angle of maximum 50°, but preferably 30° to the vertical in order to counteract potential deposits resulting from the degassing process, or to counteract other solid particles. 
     The pressure equalization line ( 11 ) for ensuring the same interior pressure in the condenser ( 1 ) and the measuring pot ( 9 ) runs from the upper region of the measuring pot ( 9 ) into the condenser interior and is preferably constructed in such a manner that no splash water from the condenser interior can get into the line, which is achieved in that the open end projecting into the condenser interior has a short section running vertically downwards. 
     Thereby it is achieved that penetrating splash water flows back into the condenser interior and does not get into the measuring pot ( 9 ) where could affect the level measurement. 
     The present invention has the following advantages over the current prior art:
         Controlling the delivery volume of the cooling water pumps instead of controlling based on a continuous level measurement.   Avoiding major level variations due to a continuous level measurement and a continuous adaption of the delivery volume of the cooling water pumps.   Energy-efficient utilization of the delivery capacity of the cooling water pumps.   Avoiding insufficient water, quantities at the intake of the pump and thus avoiding cavitation in the pumps.       

     These and other advantages are achieved by:
         Installation of a communicating container arranged outside of the condenser to calm the water surface.   Contactless level measurement by a measuring probe suitable for vacuum operation   Measured value-dependent control of a speed-controlled cooling water pump.       

       FIG. 1  serves as an example for the use of the device according to the invention in a steam-jet vacuum pump. 
     The illustrated vacuum pump stand consists of the condensers ( 1 ) and ( 2 ) with the cooling water spray nozzles ( 3 ), the steam-jet ejectors ( 5 ), ( 6 ) and ( 7 ), the condenser cooling water pumps ( 8 ) with the outer level measuring pot ( 9 ) and the measuring probe ( 10 ) arranged at the upper end of the same, and the pressure equalization line ( 11 ) running to the condenser ( 1 ), and the inclined discharge pipe ( 13 ) which runs into the condenser water down pipe ( 4 ) of condenser ( 1 ). The condenser cooling water pumps ( 8 ) convey the cooling water through return line ( 14 ) for further treatment of the cooling water, such as CO washer, settling tank, etc. which are not shown here.