[Q&A Question 166] 2017.06.15
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This post was last edited by 955559 on 2017-7-21 at 23:11. [Q&A Question 166] On 2017.06.15, when the temperature control system of a heating furnace malfunctions due to process requirements, the furnace should be shut down. Please explain the air-open and air-close types of control valves, as well as the positive and negative action modes of the regulators. (This question is an extension of a previous one; it consists of two parts: 2 points for the air-open/air-close types, 3 points for the explanation, and 2 points for the positive/negative action modes.) Explanation: 3 points. ) The reference answers will be visible after responding; points are awarded by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) In the event of a fault, the gas pressure drops to zero; therefore, the fuel supply must be cut off to ensure that the furnace shuts down. As a result, the control valve needs to be of the air-operated type, such that it closes when the gas supply is interrupted. When the furnace temperature rises, the amount of fuel required decreases, which means the valve opening needs to be reduced. Since it is an air-operated valve, the output from the regulator also needs to be decreased, so a reverse-acting regulator should be used. Scoring criteria: 2 Wealth points for incorrect attempts; 3–8 points for *incomplete* answers. 10 Wealth points for correct answers, provided with detailed explanations; 15–20 Wealth points if the answer is correct but lacks sufficient details. Please score according to these criteria. Note: If there are editing records after answering, only points will be awarded to those who participated. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have no relation to the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updating now) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updating now) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (already updated) http://bbs.hcbbs.com/thread-1597792-1-1.html
In the event of a fault, when the air supply pressure is zero, the fuel should be cut off to ensure that the furnace shuts down. Therefore, the control valve is required to be air-operated, closing when the air supply is interrupted. As the furnace temperature increases, a reduction in the fuel volume is required, that is, the opening degree of the control valve must be decreased. Since it is a pneumatic on-off valve, a reduction in the regulator output is required, so a feedback regulator should be used. The operation process of the control system is as follows: feed decreases, temperature rises, the regulator’s output drops, the control valve closes further, fuel supply decreases, and the furnace temperature falls ； Conversely, if the furnace temperature drops for various reasons, the regulator’s output increases, the control valve opens wider, the fuel supply increases, and the furnace temperature rises.
The control valve is air-operated and closes when the air supply is interrupted. As the furnace temperature increases, a reduced fuel supply is required, which means decreasing the opening degree of the control valve. Since it is a pneumatically operated valve, a reduction in the output of the control valve is required, so a reverse-acting regulator should be used.
The control valve is a air-operated valve that shuts off in the event of a fault, thereby ensuring safety. The regulator operates in a direct-acting manner, delivering an output signal proportional to the input signal.
In the event of a fault, when the air supply pressure is zero, the fuel should be cut off to ensure that the furnace shuts down. Therefore, the control valve is required to be air-operated, closing when the air supply is interrupted. As the furnace temperature increases, a reduced fuel supply is required, which means decreasing the opening degree of the control valve. Since it is a pneumatic on-valve, a reduction in the regulator output is required, so a feedback regulator should be used. The operation sequence of the control system is: feed-in ↓→ temperature ↑→ regulator output ↓→ valve opening degree ↓→ fuel volume ↓→ furnace temperature ↓. Conversely, due to various reasons, the furnace temperature ↓→ the regulator output ↑→ the opening degree of the control valve ↑→ the fuel supply ↑→ the furnace temperature↑
The control valve is air-operated and closes when the air supply is interrupted. As the furnace temperature increases, a reduced fuel supply is required, which means decreasing the opening degree of the control valve. Since it is a pneumatically operated valve, a reduction in the output of the control valve is required, so a reverse-acting regulator should be used. The operation process of the control system is: feed intake ↓→ temperature rises ↑→ regulator output decreases ↓→ opening degree of the control valve decreases ↓→ fuel quantity decreases ↓→ furnace temperature drops. Conversely, due to various reasons, the furnace temperature ↓ → the regulator output ↑ → the opening degree of the control valve ↑ → the fuel supply increases ↑ → the furnace temperature rises.
In the event of a fault, the gas supply pressure drops to zero; therefore, the fuel supply must be cut off to ensure that the furnace shuts down. As a result, the control valve needs to be of the air-operated type, such that it closes when the gas supply is interrupted. When the furnace temperature rises, the amount of fuel required decreases, which means the valve opening needs to be reduced. Since it is an air-operated valve, the output from the regulator also needs to be decreased, so a reverse-acting regulator should be used.
A fault requires the fuel to be cut off to ensure shutdown; therefore, the control valve should be of the air-operated type, closing when the fuel supply is interrupted. As the furnace temperature rises, it is necessary to reduce the amount of air supplied, which means the flow rate through the control valve should decrease; hence, the control valve is of the reverse-acting type.
Air-operated control valve: it opens when there is air flow and closes when there is no air flow
In the event of a fault, when the air supply pressure is zero, the fuel should be cut off to ensure that the furnace shuts down. Therefore, the control valve is required to be air-operated, closing when the air supply is interrupted. As the furnace temperature increases, a reduced fuel supply is required, which means decreasing the opening degree of the control valve. Since it is a pneumatically operated valve, a reduction in the output of the control valve is required, so a reverse-acting regulator should be used.