Oxyfuel Boiler Primary Gas Flow Control
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Solution Overview
Problem
Oxyfuel combustion boilers face challenges in achieving stable combustion due to the absence of a suitable indicator for controlling the primary air flow rate, as conventional air-combustion boilers rely on the A/C ratio, which is not applicable in oxyfuel systems.
Innovation Solution
The method involves controlling the flow rate of primary recirculating exhaust gas in oxyfuel combustion boilers by defining a new ratio, G/C, which ranges from 2.0 to 6.0, using a system comprising sensors and regulators to maintain stable combustion, including a CO2 density monitor, O2 density monitor, flowmeter, flow regulator, and controller to adjust the G/C ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the A/C ratio is used to control primary air flow rate in oxyfuel combustion boilers, then combustion stability can be maintained in conventional air-combustion systems, but the indicator becomes inapplicable and combustion stability cannot be achieved in oxyfuel systems
Solution Approach 1:
The invention changes the control parameter from the conventional A/C ratio (primary air flow rate to coal amount) to a new parameter G/C (primary recirculating exhaust gas flow rate to coal amount). This parameter substitution adapts the control system to oxyfuel combustion conditions where primary air is replaced by recirculating exhaust gas, thereby maintaining combustion stability in the new combustion system
Solution Approach 2:
Instead of controlling primary air flow rate as in conventional systems, the invention inverts the approach by controlling the flow rate of recirculating exhaust gas that replaces the primary air. This inversion of the control target enables the system to achieve stability through the new combustion mechanism of oxyfuel combustion
2Reliability
If the flow rate of primary recirculating exhaust gas is not properly controlled, then combustion stability cannot be maintained, but excessive control complexity increases system cost
Solution Approach 1:
The control system uses a unified G/C ratio parameter that serves multiple functions: it controls the primary recirculating exhaust gas flow rate, ensures stable combustion, and prevents flame blowout. This single parameter approach simplifies the control system while achieving multiple objectives simultaneously
Solution Approach 2:
The invention implements feedback control by monitoring the actual G/C ratio and adjusting the primary recirculating exhaust gas flow rate to maintain the ratio within the optimal range of 2.0 to 6.0. This closed-loop control ensures combustion stability without requiring overly complex control mechanisms
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 stable combustion in oxyfuel combustion systems by using the G/C ratio as a new indicator, ensuring the flow rate of primary recirculating exhaust gas is within the optimal range, thereby preventing flame blowout and maintaining combustion stability.
Implementation Method 1
a CO2 density monitor for sensing CO2 density of the primary recirculating exhaust gas to be led to the mill
Implementation Method 2
an O2 density monitor for sensing O2 density of the primary recirculating exhaust gas to be led to the mill
Implementation Method 3
a flowmeter for sensing the flow rate of the primary recirculating exhaust gas to be led to the mill
Implementation Method 4
a flow regulator for regulating the flow rate of the primary recirculating exhaust gas to be led to the mill
Implementation Method 5
a controller for calculating specific gravity of the primary recirculating exhaust gas on the basis of the CO2 and O2 densities sensed by the CO2 and O2 density monitors, respectively
Data Source
AI summary
Provided are a method and an apparatus of controlling a flow rate of a primary recirculating exhaust gas in an oxyfuel combustion boiler, capable of realizing a stable combustion by a burner in oxyfuel combustion. Weight ratio of flow rate of primary recirculating exhaust gas [ton/h] to amount of pulverized coal from a mill [ton/h] is defined as G/C, and the flow rate of primary recirculating exhaust gas is controlled so that the G/C falls within a given range.