Document kDxEVDVxM2KrOX2GG9EEG9pJb

Thomas G. Grumbles T S ^: ItcP V1S1A 7Date 6 ^'7been lAVll>l\/eCi >*\ <5^ h iLCCp VVV 000015340 V RECEIVED JULIO '86 To: G. L. FOSHEE, Westlake, LA. Route: ____ Interoffice Communication From: Dote: Subject: G. W. BACON, Houston, TX. July 11, 1986 H2S IN REFINERY FUEL GAS Hydrogen sulfide in refinery fuel gas obtained from Conoco poses potential safety problems for workers in the Lake Charles chemical complex. Currently Conoco is to inform Vista when H^S content in the refinery fuel gas exceeds 100 ppm. PED has been requested to verify the existing standard and make recommendations as necessary. The current 100 ppm limit for notification appears to be based on SO permit limits for burning RFG in the VCM or LAB plants. (E. 0. Strand-IOC-4/8/86). Conoco refinery off gas specifications are for a normal concentration of H_S at 25 ppm and a maximum concentration of 80 ppm. See Table I. It should always be assumed that H^S is present in the refinery fuel gas. The 100 ppm limit is also acceptable from a safety standpoint. Based on published data, exposure to in concentrations up to 100 ppm, for short time periods, does not cause permanent injury. If the pipeline concentration is 100 ppm, there is little chance of a worker being exposed to at this concentration unless there is a significant leak. However at concentrations above 100 ppm, H^S deadens the sense of smell. It would be possible for a worker to attempt to fix a leak when the H,,S concentration is high enough to kill without being able to detect the presence of ^S. Therefore, Vista should be informed when the concentration exceeds 100 ppm. Table II shows the effect of on humans for various concen tration levels. There are several potential problem areas for hydrogen sulfide within the plant. These problem areas include: 1.) Blowdown of the steam plant fuel gas drum , and 2.) Leakage from valves and fittings within the area. Blowing down the fuel gas drum involves forcing accumulated water in the fuel gas drum into a containment vessel. The water contains dissolved H^S which is highly corro sive. Corrosion could cause leaks in the blowdown line or possible rupture of this line. Leakage from valves and fittings is probably the source of detectable hydrogen sulfide in the area. If pipeline concentrations become excessive, concentration levels could exceed the threshold limit value (TLV) of 10 ppm. It is necessary that plant personnel be aware of excessive H^S levels in the fuel gas so that appropriate safety precautions can be taken. VVV 0000133*1 021/PED4 G. L.Foshee July 11, 1986 Page 2 We also evaluated systems for detecting H^S in refinery fuel gas. Two methods exist for such a detection system. The first method includes an "On-Line" analysis of H^S in the refinery fuel gas pipeline. The second method involves placement of ambient air sensors at strategic locations within the steam and ethylene plants. Under normal conditions refinery fuel gas H^S content does not pose a safety problem. The advantage of an "On-Line" detection system is that when an upset occurs, potential safety problems are imme diately identified. The usefulness of the "On-Line" system is dependent on the accuracy and timing of reports received from Conoco. If several hours elapse before Vista is informed, then Vista should consider purchasing an "On-Line" detection system. The primary disadvantage to "On-Line" analysis is that it does not provide information on the exposure level to workers in the area on a continuous basis . Plant personnel are presently investigating various options for an "On-Line" analysis system. Table III gives information and purchase price of several systems on the market. The advantage of ambient air sensing is that the concentration of which workers are exposed is a known quantity. A warning can be given at the TLV, 10 ppm, and an evacuation alert at the maximum peak concentration, 50 ppm. One disadvantage is that if Conoco does not report an upset condition, workers could be exposed to concentrations as high as 1000 ppm if an accident were to occur while working in the area. This could occur before an ambient air system could give adequate warning. Also, complete ambient air monitoring around the refinery fuel gas network would be more expensive than "On-Line" monitoring. Total cost of an ambient air system is dependent on the number of sensors employed. The average cost for ambient air sensing is about $1500/sensor. In conclusion, Vista should be informed when the H^S concentration in the refinery fuel gas exceeds 100 ppm for three reasons.1 2 3 1. H_S deadens the sense of smell above 100 ppm. 2. 100 ppm is the limit for burning RFG at the LAB and VCM plants. 3. 100 ppm is above the maximum concentration specified in contracts. 021/PED4 VVV 000015342 G. L. Foshee July 11, 1986 Page 3 In addition, plant personnel should determine if the present warning system from Conoco is adequate for pipeline concentrations of If not, Vista should proceed with plans for an "On-Line'1 hydrogen sulfide detection system. "On-Line" detection offers several advantages over ambient air monitoring. It offers the earliest warning for potential problems, it is less expensive, and it covers the entire refinery fuel gas network. If there are any questions or comments, please call me. G. W. Bacon /mb Attachments cc: JAD, THH, RHG, PDC, RJS, RLP, JCS, BHS, SAR SSP, DDZ, JCL, JV LRB CRD, FEL, PFF, TWH, TGG File: A-128.3 - LCCP - LAB - Houston 021/PED4 VVV 000015343 TABLE I GAS SPECIFICATION CONOCO REFINERY OFF GAS Total Sulfur, gr/MCF PPM H-0, dew point F , LB H20/MMCF HEAT CONTENT HHV, BTU/SCF LHV, BTU/SCF COMPOSITION, MOL % N2 C2 CO H2 C1 C2 C2 C3 C3 C4 IC4 NC4 MAXIMUM 50 80 - 35 10 1160 1060 MINIMUM 0 0 - 100 1 900 810 LOW BTU 1.7 0.2 1.0 24.9 59.8 2.4 9.8 0.1 0.1 0 0 0 100.0 TYPICAL 10 - 20 16 - 32 - 50 5 1100 1000 NORMAL 1.6 0.2 0.6 17.0 51.8 5.0 20.5 1.9 1.4 0 0 0 100.0 021/PED4 VVV 000015344 TABLE II EFFECTS OF HYDROGEN SULFIDE INHALATION ON HUMANS^ CONCENTRATION (PPM) 1000 + 200 - 1000 100 - 200 25 - 100 1 - 25 10 50 EFFECT (Less Than Twenty Minutes) Immediate Unconsciousness, Death Unconsciousness, Respiratory Paralysis, and Possible Death Eye Damage, Burning Throat, Deadened Sense of Smell Burning Eyes, Headache, Dizziness Irritation of Eyes and Respiratory System, Rotten Egg Odor Threshold,Limit Value for Eight-Hour Exposure Maximum Allowable Peak Exposure (3) REFERENCES (1) Adapted from "Occupational Exposure to Hydrogen Sulfide" Criteria Document, National Institute of Occupational Safety and Health, (NIOSH), May 1977. (2) NIOSH Standard (3) OSHA Standard yVV 0000153^5 021/PED4 TABLE III ON-LINE H,,S DETECTION SYSTEMS MANUFACTURER: METHOD: DESCRIPTION: RANGE: ADVANTAGES/ DISADVANTAGES: PRICE: Tracor Atlas Inc. Lead Acetate Tape contacts lead acetate sensing tape. Lead sulfide forms and tape darkens. Rate of darkening, which is detected by light deflec tion is proportional to H^S concentration. 20 ppb 100% This system is widely used and is specific. The mechanical tape drive is subject to breakdown. Tape must be replaced every two weeks. Three minute measuring cycle. This system is employed by Conoco. $13,000 MANUFACTURER: METHOD: DESCRIPTION: RANGE: ADVANTAGES/ DISADVANTAGES: PRICE: I.T.T. Barton Titration Hydrogen sulfide is titrated by a bromine reagent. The reagent is generated by passing a current through an electrolytic solution. Excess reagent is maintained in the solution by the generating current. Net generating current is proportional to H^S concentration. 0 - 1000 ppm Must use a filter to make H^S specific. Bromine solution must be replaced every two weeks. $10,000 021/PED4 vvv 000015346 TABLE III (Con't.) MANUFACTURER: METHOD: DISCRIPTION: RANGE: ADVANTAGES/ DISADVANTAGES: PRICE: Texas Analytical Solid State Sensor Sensor detects by diffusion/adsorption. Interaction between the sensor and results in a decrease in resistance proportional to the H^S concentration. Any Range within 0-1% Lower cost, continuous analysis $4,600 MANUFACTURER: METHOD: RANGE: ADVANTAGES/ DISADVANTAGES: PRICE: Western Research Inc. UV Adsorption 0-25 ppm Not suitable for RFG, low range and high cost $19,500 021/PED4 ,,VV 000015347