다음 내용은 Hydrocarbon Processing July 1995에 실린 내용의 일부입니다.
Pump minimum flow control 관련 내용인데요.
A more efficient method of recycle control requires that the discharge flow of the pump itself
is measured, and that a valve in the recycle line is opened when the process does not draw the required minimum flow. The most straightforward way to accomplish this is shown
in Figure 1-9. Note that the recycle line tees off upstream of the control valve. It is precisely
when the control valve is closed that the recycle is needed. There is a small problem with
controlling the minimum flow in this way: The measurement orifice in the discharge consumes energy and also slightly reduces pump capacity. A second problem is that the actual signal being measured is the ∆P across the orifice plate. Since flow varies as the square root of ∆P, a minimum flow of 40% of maximum flow implies a controller whose set point is only 16% of the measurement range. A typical instrument accuracy is 1%. Therefore an error of 7% of the setpoint can be expected. Fortunately the minimum flow need not be held very accurately. Recycle control is sometimes accomplished using a local pneumatic controller mounted directly on the valve.
드릴 질문은 아래와 같습니다.
1. "an error of 7% of the setpoint can be expected" 라는 내용이 나오는데, 7%라는 숫자는 어찌 나온 걸까요? 알듯 말듯 한데, 잘 떠 오르지 않네요.
2. "local pneumatic controller" 라는 말이 나오는데, 이게 뭘까요? 경험 있으신 분 설명 부탁드립니다.
감사합니다.
