It is desired to reduce the concentration of CO₂in the flue gas from a coal-fred power plant, in order to reduce greenhouse gas emissions. The effluent flue gas is sent to an ammonia scrubber, where most of the CO₂is absorbed in a liquid ammonia solution, as shown in Fig. E15.3. A feedforward control system will be used to control the CO₂concentration in the flue gas stream leaving the scrubber C_CO2which cannot be measured on-line. The flow rate of the ammonia solution entering the scrubber Q_Acan be manipulated via a control valve. The inlet flue gas flow rate Q_Fis a measured disturbance variable.
(a) Draw a block diagram of the feedforward control system. (It is not necessary to derive transfer functions.)
(b) Design a feedforward control system to reduce CO₂ emissions based on a steady-state design (Eq. 15-40).

Available Information:
(i) The flow sensor-transmitter and the control valve have negligible dynamics.
(ii) The flow sensor-transmitter has a steady-state gain of 0.08 mA/(L/min).
(iii) The control valve has a steady-state gain of 4 (gal/min)/mA.
(iv) The following steady-state data are available for a series of changes in Q_A:

Q_A (gal/min)                         C_CO2 (ppm)
15.................................................125
30..................................................90
45..................................................62

(v) The following steady-state data are available for a series of changes in Q_F,

Q_F (L/min)                                C_CO2 (ppm)
100.................................................. 75
200.................................................. 96
300.................................................. 122

Transcribed Image Text:

Flue gas Out Ammonia In Scrubber Flue gas In Ammonia Out Figure E15.3