Water Recirculation for SCR Temperature Control
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Solution Overview
Problem
Existing selective catalytic reduction (SCR) systems in power plants are designed to operate within a narrow temperature range, making it challenging to maintain optimal nitrous oxide emission control when power plants operate at loads below maximum continuous rating, as they often do for most of the year, due to stringent emission regulations, and replacing or modifying these systems is economically and practically infeasible.
Innovation Solution
A water recirculation system that diverts water from a downcomer to a tapoff line and transports it to an economizer, allowing for precise control of exhaust gas temperature by mixing it with colder feedwater, thereby maintaining the temperature within the SCR system's operating range without requiring extensive retrofitting or new equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SCR systems are designed to operate within a narrow temperature range, then emission control effectiveness is improved, but adaptability to various power plant load conditions deteriorates
Solution Approach 1:
The patent changes the thermal parameters of the flue gas by introducing cold feedwater into the economizer. This parameter change allows the SCR system to receive flue gas within its optimal temperature range (620-700°F) even when the power plant operates at low load conditions that would otherwise produce flue gas below this range. The feedwater injection adjusts the flue gas temperature to match the SCR system's operational requirements.
Solution Approach 2:
The patent introduces feedwater as an intermediary substance that mediates between the low-temperature flue gas produced at low load and the SCR system's minimum operating temperature requirement. The feedwater acts as a thermal regulator, absorbing or releasing heat to bring the flue gas temperature into the acceptable range for SCR operation, thereby enabling the SCR system to maintain effectiveness across varying load conditions.
2Adaptability or versatility
If new SCR systems are installed to operate at wider temperature ranges, then adaptability to various load conditions is improved, but device complexity and installation cost increase
Solution Approach 1:
The patent utilizes existing feedwater that is already available in the power plant's water system and directs it to the economizer through a simple injection mechanism. This self-service approach eliminates the need for separate temperature control systems or additional complex equipment. The existing feedwater serves dual purposes: maintaining boiler water levels and regulating flue gas temperature for SCR operation.
Solution Approach 2:
The patent makes the existing feedwater system multi-functional by having it serve both its traditional purpose (boiler water make-up) and a new function (flue gas temperature control). This universal utilization of existing resources avoids the need for dedicated temperature control equipment, thereby reducing device complexity and installation costs while achieving wider effective temperature range capability.
3Temperature
If feedwater is injected into the economizer, then backend gas temperature control is improved, but water flow management complexity increases
Solution Approach 1:
The patent merges the feedwater injection function with the existing economizer structure and water circulation system. By integrating the temperature control function into the existing economizer rather than adding a separate system, the patent avoids creating additional complex water flow management infrastructure. The injection point is incorporated into the existing water flow path through the economizer.
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
The water recirculation system effectively maintains backend gas temperatures within the SCR system's operating range at various power plant loads, reducing the need for costly upgrades and allowing for efficient operation across different load conditions with minimal design modifications, using few moving parts and avoiding expensive ductwork changes.
Implementation Method 1
an economizer link which receives water from the tapoff line and transports the water to an economizer
Implementation Method 2
transporting the water to an economizer... allowing for precise control of exhaust gas temperature by mixing it with colder feedwater
Data Source
AI summary
A water recirculation system for a steam power plant includes a tapoff line which receives water from a downcomer, and an economizer link which receives water from the tapoff line and transports the water to an economizer.