KING FAHD UNIVERSITY CHEMICAL ENGINEERING COURSE NOTES (Process Control)-sol-hw-7

KING FAHD UNIVERSITY CHEMICAL ENGINEERING COURSE NOTES (Process Control)-sol-hw-7

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 8.6 For PI control t 1 e(t ) + e(t*)dt * p (t ) = p + K c I 0 t 1 p (t ) = K c e(t ) + e(t*)dt * I 0 Since e(t) = ysp ym and ym= 2 Then e(t)= -2 t 1 2 p (t ) = K c - 2 + (-2)dt * = K c - 2 - I 0 I t Initial response = - 2 Kc Slope of early response = - - 2 Kc = 6 2K c I Kc = -3 I = 5 min - 2K c = 1.2 min-1 I 1234567898 9.1 a) Flowrate pneumatic transmitter: 15 psig - 3 psig qm(psig)= (q gpm - 0 gpm) + 3 psig 400 gpm-0 gpm psig = 0.03 q (gpm) + 3 psig gpm Pressure current transmitter: 20 mA - 4 mA Pm(mA)= ( p in.Hg - 10 in.Hg) + 4 mA 30 in.Hg - 10 in.Hg mA = 0.8 p (in.Hg) - 4 mA in.Hg Level voltage transmitter: 5 VDC - 1 VDC hm(VDC)= (h(m) - 0.5m) + 1 VDC 20 m - 0.5 m VDC = 0.205 h(m) + 0.897 VDC m Concentration transmitter: 10 VDC - 1 VDC Cm(VDC)= (C (g/L)-2 g/L)+1 VDC 20 g/L - 2 g/L VDC = 0.5 C (g/L) g/L b) The gains, zeros and spans are: Solution Manual for Process Dynamics and Control, 2nd edition, Copyright 2004 by Dale E. Seborg, Thomas F. Edgar and Duncan A. Mellichamp 9-1 GAIN ZERO SPAN PNEUMATIC 0.03psig/gpm 0gal/min 400gal/min VOLTAGE CURRENT VOLTAGE 0.8mA/in.Hg 0.205 VDC/m 0.5VDC/g/L 10 in.Hg 0.5m 2g/L 20 in.Hg 19.5m 18g/L *The gain is a constant quantity 9.2 a) The safest conditions are achieved by the lowest temperatures and pressures in the flash vessel. VALVE 1.- Fail close VALVE 2.- Fail open VALVE 3.- Fail open VALVE 4.- Fail open VALVE 5.- Fail close Setting valve 1 as fail close prevents more heat from going to flash drum and setting valve 3 as fail open to allow the steam chest to drain. Setting valve 3 as fail open prevents pressure build up in the vessel. Valve 4 should be fail-open to evacuate the system and help keep pressure low. Valve 5 should be fail-close to prevent any additional pressure build-up. ...
View Full Document

Ask a homework question - tutors are online