Once-Through Steam Generator Pump Sizing
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Solution Overview
Problem
Once-through steam generators face high acquisition and operating costs due to the need for powerful and large circulating pumps to manage high circulating mass flow densities at part-load operations, which can lead to cooling issues and inefficient steam production.
Innovation Solution
The method involves reducing the circulating pump's design mass flow by eliminating the recirculation circuit during low-load operations and adjusting feed and circulating mass flows to maintain adequate tube cooling, allowing for compact and cost-effective pump design, with a focus on linear control scenarios to manage evaporator mass flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the circulating pump is designed to handle high circulating mass flow density at part-load operations, then adequate cooling of evaporator tubes is ensured, but the pump becomes powerful and large in size with high acquisition costs
Solution Approach 1:
The patent applies dynamic control by adjusting the circulating mass flow based on load conditions. At part-load operations, the circulating mass flow is reduced compared to full-load conditions, allowing the pump to be sized for lower capacity while still maintaining adequate cooling through optimized flow distribution and thermodynamic conditions in the evaporator tubes.
Solution Approach 2:
The invention changes the operating parameters of the circulating pump based on load conditions. By reducing the circulating mass flow density at part-load operations (from the conventional design basis), the pump can be designed with smaller size and lower power requirements while maintaining reliable tube cooling through the modified flow regime and thermal conditions.
2Device complexity
If the circulating mass flow is reduced at low-load operations, then the circulating pump can be smaller and less expensive, but cooling problems may occur due to reduced flow through evaporator tubes
Solution Approach 1:
The patent modifies the operating parameters by reducing the circulating mass flow density at part-load conditions compared to conventional designs. This parameter change allows smaller pump sizing while maintaining adequate cooling through optimized thermal-hydraulic conditions in the evaporator, where the reduced flow is compensated by improved heat transfer characteristics and temperature gradients.
Solution Approach 2:
The invention applies local quality optimization by ensuring that the reduced circulating flow is distributed and utilized effectively in the evaporator tubes. The system maintains reliable cooling by optimizing the local flow conditions and heat transfer characteristics in the evaporator section, allowing the overall system to use less circulating flow while still protecting the tubes adequately.
3Device complexity
If recirculation is eliminated during low-load operations, then pump size and acquisition costs are reduced, but thermal load on superheater heating surfaces increases due to lower fluid temperatures
Solution Approach 1:
The patent applies dynamic adjustment of the recirculation flow based on load conditions. Instead of completely eliminating recirculation, the system dynamically reduces the circulating mass flow at part-load operations to an optimized level that balances pump size reduction with maintaining adequate thermal conditions in the superheater, avoiding excessive thermal loads while still achieving compact pump design.
Solution Approach 2:
The invention optimizes the recirculation parameter (circulating mass flow) at part-load conditions to achieve a compromise solution. By setting the circulating flow at an optimized reduced level rather than eliminating it completely, the system reduces pump size and costs while maintaining sufficient fluid temperature to prevent excessive thermal load on the superheater heating surfaces.
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 enables safe and efficient part-load operation with reduced circulating pump size and cost, ensuring adequate cooling and steam production, even at low loads, while maintaining full-load performance by adjusting mass flow ratios.
Implementation Method 1
the flow medium, usually supplied in the form of feedwater, is forced through the preheater, the evaporator and the superheater provided as a rule by a correspondingly powerful feedwater pump
Implementation Method 2
in which a feed mass flow of a flow medium is fed to the evaporator with the aid of a feed pump and is at least partially evaporated there
Implementation Method 3
non-evaporated flow medium being separated in a separator downstream of the evaporator
Implementation Method 4
a circulating mass flow of the separated flow medium is fed back into the evaporator with the aid of a circulating pump
Implementation Method 5
the flow medium is heated up to the saturated steam temperature, the evaporation and the subsequent overheating take place continuously in one pass
Data Source
AI summary
Method for operating a once-through steam generator (2) comprising an evaporator (4), in which a feeding mass flow (SM) of a flow medium (M) is supplied with the aid of a feed pump (12) to the evaporator (4) and at least partially evaporated there, wherein flow medium (W) that has not evaporated is separated in a separator (18) arranged downstream of the evaporator (4) and a circulating mass flow (UM) of the separated flow medium (W) is returned with the aid of a circulating pump (24) to the evaporator (4), and so the mass flow referred to as the evaporator mass flow (VM) of the flow medium (M) flowing through the evaporator (4) is additively made up of the feeding mass flow (SM) and the circulating mass flow (UM). It is thereby provided that in a low-load interval (I) the feeding mass flow (SM) is increased with increasing load (L) while the circulating mass flow (UM) is kept substantially constant, in a moderate load interval (II) the feeding mass flow (SM) is further increased with increasing load (L) and the circulating mass flow (UM) is reduced to zero, and optionally in a high load interval the feeding mass flow (SM) is further increased with increasing load (L) and the circulating mass flow (UM) is kept at zero. The invention also relates to a once-through steam generator that is particularly suitable for carrying out the method.