HAZOP_GUIDE_BRITISH_STANDARD_IEC_61882_2001

4 oil vaporizer the oil vaporizer consists of a

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: oil enters the heating coil as a liquid, is evaporated, and leaves the coil as a superheated vapour. The natural gas entering the burners combines with external air and burns in a hot flame. The combustion gases leave through the stack. The oil flow is controlled by a flow control set which includes: a flow control valve, FCV, a flow element, FE, that measures the oil flow, a flow controller, FC, and a low flow alarm, FAL, which alarms if the oil flow reduces below a set point. The natural gas flow passes through a self-actuating pressure-reducing valve, PRV, to the main burner control valve TCV, and a pilot valve PV. The main burner control valve is actuated by the temperature controller TC which receives the signal from the temperature element TE, which measures the oil vapour discharge temperature. The high/high pressure switch, PSHH on the natural gas line is interlocked, via I-4 to close the main burner control valve, TCV, if the gas pressure is too high. There is also a high temperature switch, TSH, on the vaporized oil outlet to close the main burner control valve, TCV, if the oil is superheated above a maximum temperature. Finally, there is a flame detector device (not shown) which will close both gas valves should the flame go out. 52 25 25 © BSI 28 1002−80ISB © 1002−80 ISB August 2001 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI 6 8812 E I2:C100 © BSI 28 August 1002−80 ISB © 2001 Table B.6 – E xample HAZOP worksheet for oil vaporizer STUDY TITLE: O IL VAPORIZER Drawing No. : REVISION No.: DATE: TEAM COMPOSITION: M G, NE, DH, EK, LB MEETING DATE: DESIGN INTENT: No. Guide word Element Deviation Possible causes Consequences Safeguards Comments Actions required Action by 1 No Oil flow No oil flow – S upply failure F low control valve PCV closed Vaporizer coil overheats and may fail Low flow alarm FAL Safeguard depends on quick operator response Consider low flow element FE to close main burner valve TCV LB – Oil in vaporizer will boil: Low flow alarm FAL NE Possible overheating and coking of heating coil High temperature trip TSH Check whether these safeguards are adequate and the ease with which the coil could be cleaned Unvaporized liquid oil fed to the process None – I nvestigate effect of liquid oil on the process DH – C onsider interlocking the furnace flame out signal with closure of FCV – C onsider providing a low oil outlet temperature alarm – 2 No Heat No heat P lugging of coil – B lockage downstream of vaporizer Flame out in the furnace Inputs: Activities: O il flow from the feed line, heat from the furnace V aporize, superheat and transfer oil vapour to the process High temperature trip TSH – 0 15 – PART CONSIDERED: V aporizer coil from oil inlet (before flow measurement), to vapour exit to process (after temperature control) BS IEC 61882:2001 53 35 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI Element Deviation Possible causes Consequences Safeguards 3 More Oil flow More oil flow − O il delivered at higher pressure None − F ailure of flow controller FC May overload vaporizer, resulting in insufficient heating of oil stream (see point 6) – V aporizer coil overheats: possible coking of oil and plugging High temperature switch TSH closes main burner valve TCV Review safeguards of gas flow controls EK – O il vapour at too high temperature delivered to the process High temperature switch TSH closes main burner valve TCV Check the effect of high vapour temperature on process DH − 4 More Heat More heat Comments Furnace temperature too high Action by – C heck capability of FCV to control flow of oil at higher pressure MG – W rong set point of FC Actions required C onsider providing a low oil outlet temperature alarm – 0 17 – Guide word 6 8812 E I2:C100 No. BS IEC 61882:2001 54 45 Table B.6 ( continued) 5 Less Oil flow Less oil flow Low delivery pressure Same as point 4 Same as point 1 Safeguards adequate No action 6 Less Heat Less heat Low output from furnace May fail to vaporize or superheat oil. Oil with low temperature delivered to process None Does this matter? Check the effect of unvaporized or low superheat oil on process DH Consider providing a low oil outlet temperature alarm EK © BSI 28 August 2001 1002−80 ISB © Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI 6 8812 E I2:C100 © BSI 28 August 1002−80 ISB © 2001 Table B.6 ( continued) No. Guide word Element Deviation Possible causes Consequences Safeguards 7 As well as Oil As well as oil Impurities in oil, e.g. Rapid boiling of water may eject liquid oil into process Comments Actions required Action by None Check potential water content of oil DH – W ater – S olids, nonvolatiles, corrosives or unstable compounds in oil Potential for partial or complete plugging of coil (see point 1), carbon layer, or corrosion and leakage (see point 11) None Check potential impurities DH Reverse Oil flow Reverse flow Loss of feed may permit back-flow of oil vapour from the process into the coil and the oil feed system Possible overheating of feed and damage to feed system None Review implications on unit and consider installing back flow prevention DH 9 Other than Oil Other than oil Totally wrong material fed to vaporizer Depends on material Upstream control of inputs...
View Full Document

Ask a homework question - tutors are online