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13/1, City Heart, 67 Naya, Paltan, Dhaka, Bangladesh
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傳真：880-2-9331527
Steam pressure reducing station
產品型號：PREDU & Pneumatic Control
產品特色
Pressure control A steam pressure reducing station without auxiliary energy is shown in Fig 1. Pressure control takes place via a special control valve, the pressure reducer PREDU® (Pos. 1). This selfacting valve requires no auxiliary energy. For the operation of a pressure reducer, a series of other auxiliary and monitoring valves are required. The concept of "steam pressure reducing station" embraces all these components, including pipes.
Two distinct sets of pipes are recognised, the main pipe divided into the upstream and downstream pipe, as well as the bypass pipe. The steam flows first of all through the upstream pipe, then the globe valve FABA® (Pos. 4), the strainer (Pos. 5) and the steam trap (Pos. 3) before then reaching the pressure reducer. Following pressure reduction in the pressure reducer, it reaches a further globe valve (Pos. 6) in the downstream pipe to the station output, the safety valve SAFE (Pos. 2) being directly connected to this area. The nominal diameter of the pipe depends on the maximum admissible speed of flow
Fig. 1: Steam pressure reducing station without auxiliary energy
The exact dimensioning is described under point 3. “Technical process design". On the admission of steam, the control pipe and the water seal pot (Pos. 7) must be filled with water. The diaphragm of the pressure reducer hanging downwards together with the actuator is thus protected from the high steam temperatures. The bypass pipe is required for the manual operation of the downstream system in the case of maintenance of the strainer and the pressure reducer. For this purpose, globe valves in front and behind the pressure reducer are closed and the globe valve in the bypass pipe (Pos. 8) is opened. Watching the manometer (Pos.10), the operation is to be maintained manually, with the safety valve performing the task of pressure protection in this case as well.
In steam operation, condensate constantly forms in the pipes and must removed via the steam trap. Fig 1 clearly shows the diversion in the pressure pipe via the steam trap CONA®-S (Pos. 13). The upper globe valve (Pos. 11) is normally open and is closed only in the case of a maintenance operation on the trap, the lower globe valve (Pos.14) being provided for the removal of sludge and is normally closed. Using the sight glass (Pos. 12) it is possible to observe the flow of condensate and thus to control the functioning of the trap. Condensate also forms in the downstream pipe. In particular in the case of a small flow and a almost closed pressure reducer, the condensate level can rise. In the case of a pressure reducer suddenly opened by increased output demand, water hammer occurs, which in principle is to be avoided. Fig. 1 shows the outflow using a bimetallic steam trap CONA®-B (Pos. 17).
For controlling the reducing station, gauges in front and behind the pressure reducer are useful and the inlet pressure between the strainer and the pressure reducer should be measured, since a blockage of a strainer can be recognised by a pressure drop. For simplifying the setting and an easier recognition of any disruption, it is useful to arrange the measurement of the minimum pressure in the proximity of the pressure outlet point of the control pipe.
Fig 2 shows a pressure reducing station with auxiliary energy, where instead of a pressure reducer, a pneumatic control valve (Pos.1) is introduced. In place of a outlet pressure pipe with a water seal pot, the pressure to be controlled is measured by a sensor and taken to an SPS control. Here, the actual measured value is compared with the preset value and the resulting control signal (e.g. 4-20 mA) is taken to the positioner of the control valve. In addition to the electrical energy for the SPS control and the positioner, the control valve requires a further source of auxiliary energy, in this case compressed air. In contrast with the pressure reducing station, the remaining valves are the same without auxiliary energy and are also needed to perform the same functions.
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