INSTRUMENTATION FOR P&ID’s Learning Objectives Be Able to Interpret Controls Symbology Know what the physical manifestation of the symbology is Know the parts of a ‘control loop’ Know what a Control Valve looks like and how it works Be able to look at a control scheme and understand how it works Be able to design some basic control schemes Instrumentation Cookbook Instrumentation Why Are We Doing This For this Project ChemEcon – Includes Controls in ‘factors’ ChemEcon – To Size The Pumps We Need To Include “Inline” Instrumentation pressure drop FE PI Instrumentation Cookbook Control Loop A Simple Feedback Control Loop Set Point Often not shown Measured Variable (temp, pressure, flow...) FE FIT Controller Manipulated Variable FIC FV Readout Devices Switches and Alarm Devices Self Actuated Control Valves Recording Indicating High Low Comb AR AI ASH ASL ASHL BR BI BSH BSL BSHL Controllers Initiating or First Measured Variable Letter Analysis A Burner, Combustion B Users Choice C Users Choice D Voltage E Flow Rate F Flow Quantity FQ Flow Ratio FF Users Choice G Hand H Current (Electrical) I Power J Time K Level L Users Choice M Recording Indicating blind ARC AIC AC BRC BIC BC Transmitters Recording Indicating Blind ART AIT AT BRT BIT BT Instrumentation Naming ERC FRC FQRC FFRC EIC FIC FQIC FFIC IRC JRC KRC LRC HIC IIC JIC KIC LIC EC FC FCV FICV FFC ER FR FQR FFR EI FI FQI FFI ESH FSH FQSH FFSH ESL FSL FQSL FFSL HR IR JR KR LR HI II JI KI LI ISH JSH KSH LSH ISL JSL KSL LSL ESHL FSHL Instrument Society Of America (ISA) Initiating or First Measured Variable Letter Analysis A Burner, Combustion B Users Choice C Users Choice D Voltage E Flow Rate F Flow Quantity FQ Flow Ratio FF Users Choice G Hand H Current (Electrical) I Power J Time K HC KC LC KCV LCV Solenoids, Relays, Computing Primary Devices Element AY AE BY BE EY FY FQY HY IY JY KY EE FE FQE FE Well Of Test Point Probe AP AW BW FP Viewing Device, Glass HS ISHL JSHL KSHL LSHL Safety Device BG FG IE JE KE ISA Typical Letter Combinations.xls ERT FRT EIT FIT FQIT ET FT FQT HRT IRT JRT KRT LRT HIT IIT JIT KIT LIT HT IT JT KT LT Final Element AV BV EZ FV FQV FFV HV IZ JV KV Instrumentation Cookbook P&ID’s - Symbology Equipment Symbology Instrumentation Symbology See the document “P&ID Symbols and Photos.DOC” Instrumentation Cookbook P&ID’s - Symbology LIC Located in DCS (process control computer) Software Signal LT Physically located ‘in field’ Physical wire “hardwired” Instrumentation Cookbook Signal The “Control Valve” Elec To valve (4-20 mA DC signal) Actuator driven by Compressed Air Valve Instrumentation Cookbook The “Control Valve” Control Valve Sizing CV vs % Opening Characteristic CV Volumetric_Flow Volumetric_Flow gal min Pressure_Differential Spec_Gravity Pressure_Differential Pressure Drop psi Flow Rate Instrumentation Cookbook The “Control Valve” CV vs % Opening Characteristic Cv % open Instrumentation Cookbook Typical Controls Level Flow Pressure Temperature Composition Instrumentation Cookbook Level Control Purpose Prevent the tank from overfilling / running dry LT LIC LV Instrumentation Cookbook Level Control Purpose Hold a liquid “Seal” LT LIC No Gas! LV Instrumentation Cookbook Level Control Purpose Prevent pump from running dry and thus being destroyed RO LT LIC LV Note: - valve always on disch to prevent flashing on pump suction - pump may also require a minimum flow bypass Control Systems Aside - Speed Measured Variable can be slow to measure (i.e. the composition using an analyser) or, fast (i.e. pressure) The Manipulated Variable can be slow too i.e. adjusting the hot water tap in your shower The level in a tank can take hours to change (slow) Control Systems Aside - Speed Slow Things Say > few seconds Reducing Pressure by Opening a valve on a large gas filled tank Measure Composition (analysers) Change Level In Large Tank Fast Things Less than a second Measure Pressure Measure Flow (Diff Press) Measure Temp (?) But…. It’s all RELATIVE !! Instrumentation Cookbook Flow Control Purpose: Ensure steady material flow rate Smooth feed to columns Set Production rate Fast to Measure Flow Changes usually require a control valve to change it’s position which can take seconds. Vapour systems have a ‘capacitance’ that need to be overcome before the flow changes are experienced everywhere in the system Instrumentation Cookbook Flow Control FT FIC FE M FT FIC I FE FV SIC Variable Speed Drive Mount FE upstream in vapour systems to minimize pressure/density effects Instrumentation Cookbook - Ratio Flow Control SP FIC FT FE FRIC FV FIC SP FT FE SP Set one flow rate Other flow is proportionally controlled to first flow Ensure correct mixture / recipes FV Instrumentation Cookbook Pressure Control Similar to Level (control of material inventory) Very fast for incompressible fluids Hard to say for compressible fluids, depends on system volume but probably slow Instrumentation Cookbook Pressure Control Control Upstream | Control Downstream PIC PIC PT PT PV Need to control vessel pressure PV Need to downstream (header or process) pressure Instrumentation Cookbook Pressure Control Condensable Gas PIC PV PT Need to control vessel pressure Fast or slow? Instrumentation Cookbook Pressure Control Liquid Pressure Control PIC PT PV Control pump discharge pressure - not very useful Instrumentation Cookbook Pressure Control Liquid Pressure Control PIC FIC PT FT PV Control pump discharge pressure - ensure constant feed pressure to FV FE FV Instrumentation Cookbook Temperature Control Normally control the ‘flow’ of one fluid to change the temperature of another In Reality it’s an LMTD change that affects the exchanger duty Q = U A Tln Instrumentation Cookbook Temperature Control Liquid / Liquid - control on cooling media C/w Instrumentation Cookbook Temperature Control Liquid / Liquid - control on process C/w Instrumentation Cookbook Temperature Control Steam Pressure Control T Increase Stm Pressure Instrumentation Cookbook Temperature Control Condensate Level Control Reduce flooded Area Instrumentation Cookbook Cascade Control Example - Driving to Montreal You’re driving / steering the car Someone else is telling you which roads to drive on and when to turn Instrumentation Cookbook Cascade Control One Control Loop Determines Setpoint of a Second Loop FT FE High Speed P M I Low Speed Flow SIC SP Variable Speed Drive FIC SP -Using the flow through the pump to control the rotational speed of the pump Instrumentation Cookbook Cascade Control PIC FIC FT FE FV PT Common Around Distillation Columns Where There Are Slow Loops Instrumentation Cookbook Controller Interaction Many Controllers Interact but some configurations Interfere with each other I.e. the control of reflux flow interacts with the column bottom level control but two flow controllers on the same pipe will interfere with each other (they duel for control of the flow) Instrumentation Cookbook Controller Interaction Duelling Control ? LT LIC FIC LV FT FE Instrumentation Cookbook Controller Interaction Duelling Control ? LIC LT FIC FT FE LV Instrumentation Cookbook Controller Interaction Duelling Control ? SP= 75 psig PIC SP= 35 psig PIC PT 100 psig Compressed Air PV PT PV User 1 User 2 User 3 User 1 User 2 User 3 P&ID Cookbook -By Equipment P&ID Cookbook - Pumps PI PI PRV HS I HS M Pump - Min Flow Bypass RO PI LT PI LIC LV HS I HS M Reflux Tanks Set@ Vent to Safe Locn PI From Condenser From Pump HLL = 4’-6” NLL = 3’-6” LLL = 2’-0” LLLL = 2’-0” TI LSLL I LIT LAHL LIC TO LV LALL Pump S/D To Pump Compressors - Centrifugal For our purposes treat controls as a black box But... Provide an input control signal (cascade) Remember cooling water req’d (lube system...) CWS Control From ? CWR SIC M By Vendor By Owner Requirements for Column Control Feed rate control Level control for reboiler and condensate receiver Column pressure control Two controllers, corresponding to the two degrees of freedom, to deal with the specifications in PRO/II This is a very complex topic and can only be dealt with superficially in this course Columns Composition control Pressure control Provide a control scheme to ensure Feed rate is constant or is slowly changing Level control Level control Composition control Treat the top and bottom independently of each other Columns Bottoms Put level control on bottoms outflow when outflow rate > 10 x boil up rate Put level control on Steam control boilup rate > 10 x outflow rate otherwise either scheme okay FIC FT HHLL 5 bar Stm LIT HLL NLL LLL LLLL T TE LAHL LIC TIC Low P Cond TE Columns - Overhead XIC PIC PT CWS FV CWR FIC Set@ PV PI RO FT HLL = 4’-6” NLL = 3’-6” LLL = 2’-0” LLLL = 2’-0” TI LSLL I LIT LAHL LIC PI PI LALL Pump S/D LV HS I HS M Instrumentation Cookbook Column Control How to Choose the Stream that will control Level in the reflux tank Column Overhead Control - Scheme 1 when the draw rate is 10 x > reflux rate Manipulate Distillate draw rate to control Reflux level Manipulate reflux rate to control Column Composition Instrumentation Cookbook Column Control Column Overhead Control - Scheme 2 when the reflux rate is 10 x > draw rate Manipulate Distillate draw rate to Manipulate Column Composition Manipulate reflux rate to control control Reflux Drum level Instrumentation Cookbook Tanks - Storage PRV Temperature Control May Be Required -does material freeze / boil? LAHH LSHH LY LSHH TI s I LI LSLL LAHL LIT LV I M Workshop Add the composition control to the Solvent Column overhead Hint: use the pressure and temperature Workshop Draw a P&ID, including Control Scheme for column top Explain how it works 15,420 kg/hr, 113 °C 33,316 kg/hr, 113 °C END
