Steam Generator Startup Control via Firing Rate Adjustment
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Solution Overview
Problem
Once-through steam generators face challenges during startup, as a significant amount of water flows into the water-steam separation device, leading to undesired water discharge into superheater tubes, requiring large and costly separation and discharge devices, which is not efficiently addressed by existing methods.
Innovation Solution
Adjusting the firing capacity of burners based on the filling level parameter of the water-steam separating device to slow down evaporation and reduce water discharge, by throttling heat input when evaporation begins, and subsequently increasing firing capacity after water expulsion to ensure efficient startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a minimum evaporator mass flow is maintained for sufficient tube cooling during startup, then evaporator tube cooling is ensured, but water discharge into superheater tubes occurs due to sudden volume increase from evaporation
Solution Approach 1:
The patent applies preliminary action by gradually increasing the firing capacity of burners before complete evaporation occurs, and by pre-positioning outlet valves to open automatically when water level rises in the water-steam separation device. This prevents water discharge into superheater tubes while maintaining tube cooling during startup
Solution Approach 2:
The patent employs feedback mechanisms through fill-level measuring devices that continuously monitor water levels in the water-steam separation device and automatically trigger outlet valve opening when predetermined levels are exceeded. This feedback control prevents water discharge while maintaining evaporator tube cooling during startup
2Reliability
If all components of the water-steam separation device and downstream water discharge device are dimensioned to handle maximum water flow, then water discharge is prevented, but material costs and device complexity increase significantly
Solution Approach 1:
The patent applies dynamics by using automatically controlled outlet valves that open only when water levels exceed predetermined thresholds during startup. This dynamic control allows smaller, less complex water-steam separation devices and discharge equipment, as components only need to handle water discharge temporarily during startup rather than being continuously sized for maximum water flow
Solution Approach 2:
The patent changes operational parameters by controlling firing capacity as a function of fill level parameters and by adjusting water flow rates during different startup phases. These parameter changes enable adequate tube cooling while minimizing water discharge, allowing for reduced sizing of separation and discharge components
3Object-generated harmful factors
If feed water supply is reduced to minimize water output, then water discharge is reduced, but evaporator tube cooling becomes insufficient
Solution Approach 1:
The patent applies periodic action by controlling water discharge in phases during startup: initially allowing water discharge when levels rise, then reducing discharge as evaporation stabilizes. This periodic control reduces total water discharge while maintaining adequate tube cooling throughout the startup process
Solution Approach 2:
The patent uses preliminary action by gradually increasing firing capacity and controlling water flow rates in predetermined sequences during startup. This ensures adequate tube cooling from the beginning while minimizing water discharge through controlled, phased operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the size and cost of water-steam separation and discharge devices while ensuring adequate tube cooling, allowing for a more efficient and cost-effective startup process by minimizing water entry into the superheater tubes.
Implementation Method 1
the heating of steam generator tubes provided as evaporator tubes leads to evaporation of the flow medium in the steam generator tubes in a single pass
Implementation Method 2
the heating of which leads to evaporation of the flow medium conducted therein
Implementation Method 3
a water-vapour separator which can comprise, for example, a water-vapour separator and a water bottle
Implementation Method 4
a water-steam separating device with a downstream fill-level measuring device
Implementation Method 5
superheater tubes are connected downstream of the evaporator tubes on the flow medium side, which further increase the enthalpy of the exiting steam
Data Source
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Figure 2
AI summary
The invention relates to a method for starting a continuous steam generator (1) comprising a combustion chamber (8) provided with a plurality of burners (7), a water-steam separation device (14) that is mounted downstream of the evaporator tubes thereof (12) on the flow-medium side. The amount of water flowing into the water-steam separation device (14) during the starting process is kept to a minimum so that the water-steam separation device and water supply device (14) can be compact and at the same time ensuring that the evaporator tubes (12) are cooled sufficiently. The firing power of at least one of the burners (7) is adjusted in accordance with a filling level characteristic value of the water-steam separation device (14).