Weight Flow Control with Variable Stator Vanes

A turbine-driven axial compressor is used to supply air to a blast furnace. The furnace requires a certain constant weight flow, depending upon the size of furnace and the size of the charge. An example of a possible arrangement is shown in Figure 8-40(c) and can be described as follows:

1. The compensated flow transmitter determines the process flow. It converts this quantity to a signal that is proportional to the process flow and sends it to the flow controller. The transmitter could be a pneumatic device using a venturi primary element, with compensation for pressure by a pressure element and compensation for temperature by a thermocouple. The output would be a pneumatic signal that is proportional to weight flow.

2. The flow controller amplifies the transmitter signal and sends a modified signal to the final element. Rest and rate correction factors may also be required.

3. The final element is speed control. This is accomplished with a mechanism that varies the turbine-governor speed setting.

An increase in weight flow over the set point would cause a signal to reach the governor, which would reduce the turbine speed to maintain the desired flow.

A plant air system could resemble Figure 8-40(d) where a motor-driven centrifugal compressor is used.

1. The pressure transmitter senses the process pressure and converts it to a signal that is proportional to it.

2. The three-mode pressure controller amplifies the transmitter signal and sends a modified signal to the final element.

3. The final element is a suction throttle valve that reduces the flow of air into the compressor.

A process pressure increase over a set value would cause a signal to reach the suction throttle valve and would close the valve in order to reduce the inlet pressure.

Living Off The Grid

Living Off The Grid

Get All The Support And Guidance You Need To Be A Success At Living Off The Grid. This Book Is One Of The Most Valuable Resources In The World When It Comes To When Living Within The Grid Is Not Making Sense Anymore.

Get My Free Ebook


Post a comment