GB960378A - Improvements in controls for forced flow, once through vapour generators - Google Patents

Abstract

960,378. Regulating forced flow steam boilers. HOLLANDS INGENIEURS BUREAU HIBRO. Feb. 13, 1961 [Feb. 16, 1960], No. 5534/60. Heading F4A. A control device for a forced flow, once through boiler comprises a regulating apparatus motivated in response to the value of the amount of superheat, i.e. the difference in quantum of heat possessed by an amount of vapour at a temperature measured at a point in the superheat zone of the boiler and the heat possessed by the same amount of the same vapour at the saturated temperature, the value being derived from a measurement of the temperature of vapour at that point in combination with further measurement of the physical value of pressure and vapour flow or temperature and vapour flow within the boiler, the apparatus being adapted rapidly to vary the relation between liquid input and heat input to the boiler on change of load so that the output is adjusted, with only a small time delay, to the new conditions. Fig. 1 shows a boiler in which zones C-B containing liquid, B-A containing liquid and saturated vapour and A-D containing superheated vapour may be distinguished. A temperature probe 2 is inserted into the superheat zone and transmits signals to a control 10 also receiving signals representative of output flow from a transmitter 6. The combined signal is transmitted from the control 10 to the liquid input regulator 4. A change in load results in corresponding movement of the zone B-A causing a change in temperature of the probe, the resulting signal modified by the signal from 6 so that it bears a fixed relationship to output vapour flow, motivating the regulator 4 to adjust the boiler output and restore the zone B-A to its original position. The signal from the control 10 may be arranged to override the normal boiler control. Thus as shown in Fig. 4, a control device 10 receives signals from the probe 2 via a temperature transmitter 9, from an output pressure transmitter 7 and from an output flow transmitter 6 and passes a correcting and overriding signal to a control device 11 which also receives a signal from the output flow transmitter 6. The final control 12 receives a signal representing the desired input from the control 11 and a signal representing the actual input from the input flow transmitter 5 and the resultant signal obtained by comparison of these is used to regulate the liquid input control 4. A feedback signal passes from the input flow transmitter 5 to the control 12. In a modification (not shown), two probes are inserted close together into the boiler, one in the superheat zone and one in the adjacent zone, signals from the probes are compared in the transmitter 9 and a signal representing the temperature difference is fed into the control 10. In multi-tube boilers, a control as described above may be applied to each tube individually, regulators constituted by inlet chokes on all the tubes, or the inlet choke of one tube may be fixed and the control of this used to control the feed pumps.