Flue Gas Cooler Steam Prevention via Bypass Circulation
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Solution Overview
Problem
In oxyfuel combustion boilers, the high outlet gas temperature from the air preheater poses a risk of steam production in the flue gas cooler during boiler fuel cutoff, leading to potential water hammering and damage due to heat exchange with high-temperature flue gas.
Innovation Solution
A device comprising a condenser, condensate pump, low-pressure feed-water heater, boiler feed-water pump, bypass line, steam production preventive pump, inlet and outlet cutoff valves, and a controller to manage the flow of low-pressure feed-water, preventing steam production by circulating water through a bypass line and steam production preventive water circulation line when the boiler feed-water pump stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low-pressure feed-water is used as cooling medium in the flue gas cooler, then heat recovery efficiency is improved and temperature conditions are optimized, but steam production occurs when the boiler feed-water pump stops, causing water hammering and damage to piping and valves
Solution Approach 1:
The control device detects the stop signal of the boiler feed-water pump in advance and activates the bypass pump before the feed-water pump actually stops. This preliminary action ensures continuous water circulation through the flue gas cooler, preventing steam production and water hammering before they can occur. The control device opens the bypass inlet valve and closes the main feed-water outlet valve to redirect water flow through the bypass line.
Solution Approach 2:
The bypass pump and bypass line serve as intermediary components that take over the water circulation function when the main boiler feed-water pump stops. This intermediary system ensures continuous cooling water supply to the flue gas cooler, preventing the harmful effect of steam production while maintaining the heat recovery function. The bypass system acts as a bridge to maintain system reliability during pump transition.
2Duration of action of moving object
If the boiler feed-water pump stops after fuel cutoff, then the system shuts down, but the low-pressure feed-water dwelling in the flue gas cooler is heated to produce steam causing water hammering
Solution Approach 1:
The control device is configured to activate the bypass pump and open the bypass inlet valve before the boiler feed-water pump stops, based on the stop signal detection. This preliminary action ensures that cooling water circulation continues uninterrupted during the shutdown period, preventing steam production in the flue gas cooler even when the main pump is stopping. The system prepares the bypass path in advance to handle the transition period.
Solution Approach 2:
The bypass system maintains continuous water circulation through the flue gas cooler during the shutdown transition period. By keeping the bypass pump operating and the bypass inlet valve open, the system ensures that the cooling water continuously absorbs heat from the flue gas, preventing steam production. This continuity of useful cooling action persists throughout the shutdown period until temperatures normalize.
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
Effectively prevents steam production in the flue gas cooler, thereby avoiding water hammering and adverse effects on piping and valves, ensuring safe operation during both normal and emergency shutdowns.
Implementation Method 1
an flue gas cooler which cools the outlet gas temperature on the order of about 260° C. to the temperature required for the dust removing device
Implementation Method 2
use of low-pressure feed-water with a temperature on the order of about 70-100° C. is effective from viewpoints of the temperature condition and efficiency gain due to heat recovery
Implementation Method 3
part of the low-pressure feed-water boosted in pressure by the condensate pump in the boiler low-pressure feed-water system is sent under pressure by a bypass pump to the flue gas cooler
Implementation Method 4
a condenser, a condensate pump, a low-pressure feed-water heater and a boiler feed-water pump in the order named
Data Source
AI summary
A feed-water discharge side of a condenser is connected to a feed-water entry side of an flue gas cooler through a bypass line provided with a steam production preventive pump and with an inlet cutoff valve. A feed-water discharge side of the flue gas cooler is connected to the feed-water entry side of the condenser through a steam production preventive water circulation line provided with an outlet cutoff valve. When a boiler feed-water pump is stopped in boiler fuel cutoff, the inlet and outlet cutoff valves are opened and the steam production preventive pump is activated to cause water to flow through the bypass line into the flue gas cooler, is returned through the steam production preventive water circulation line to the condenser and is circulated.