Process for operating a continuous steam generator
View Patent ↗The invention relates to a process for operating a continuous steam generator. The aim of the invention is to provide, with little technical complexity and for any operating state, a synchronous variation of the feed-water mass flow passing through the evaporator heating surface and of the heat input into the evaporator heating surface. To this end, a regulating device for the discharge of feed-water is allocated to a device for adjusting the feed-water mass flow. The control variable of said regulating device is the feed-water mass flow, while its set-point value in relation to the feed-water mass flow depends on the set-point value associated to the power of the steam generator. The actual value of the feed-water density at the entry of the pre-heater is fed to the regulating device for the discharge of feed-water as one of the input values.
1. A method for operating a continuous steam generator with an evaporator heating surface, comprising:
connecting a pre-heater upstream of the evaporator heating surface;
providing an adjusting device for adjusting a feed-water mass flow in the evaporator heating surface;
assigning a feed-water through-flow regulation to the adjusting device where a control value is the feed-water mass flow and a set-point value for the feed-water mass flow is maintained as a function of a steam generator performance; and
providing an actual value of a feed-water density at the entry of the pre-heater as an input value to the feed-water through-flow regulation.
2. The process m accordance with claim 1 , further comprising providing an actual value of the feed-water density at an exit of the pre-heater to the feed-water through-flow regulation as an additional input variable.
3. The process in accordance with claim 2 , wherein the feed water set point value is defined as:
{dot over (M)}+Δ p ·V
where:
{dot over (M)} is an actual value of the feed-water mass flow at the entry of the pre-heater,
Δ p is a change over time of an average density of the feed water within the pre-heater, and
V is a volume of the pre-heater.
4. The process m accordance with claim 3 , wherein a value for the average density of the feed water at the entry of the pre-heater is approximated by the actual value of the density of the feed water at the entry of the pre-heater.
5. The process in accordance with claim 4 , wherein a change to the average density of the feed water in the pre-heater over a duration of time is formed by a functional element with a differentiating behavior.
6. The process in accordance with claim 5 , wherein a signal corresponding to the actual value of the feed-water density at the entry of the pre-heater is switched to a lag element with a time constant of the throughput time of the pre-heater, delayed according to a thermal time constant of the pre-heater and the switched signal is connected negatively to a signal corresponding to the feed-water density at the exit of the pre-heater.
7. The process in accordance with claim 6 , wherein a lag time and the thermal time constant of the pre-heater are adapted reciprocally to a load of the steam generator.
8. The process in accordance with claim 7 , wherein the feed-water through-flow regulation is switched on and off as required.