KHABAROVSK REFINERY HYDROPROCESSING PROJECT PLANT SAFETY TRAINING COURSE APRIL 29th – MAY 3rd 2013, MADRID, SPAIN
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL All operating personnel must fully understand the principles of safe plant control and correct operating procedures: in this plant, reactants as well as reaction products and their intermediates are highly toxic and therefore hazardous. All gases must therefore be treated with utmost care. The use of all safety equipment (e.g. masks, breathing apparatus, etc.) must be well known by the personnel involved with plant operations and maintenance. Carelessness, negligence or ignorance of danger are often the causes of H2S and SO2 poisoning.
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL Operators must be introduced to avoid inhalation of gas whenever possible, they should not stay unnecessarily without protection under process gas lines or equipment since H2S and SO2 are gases heavier than air. Suitable sensors are located in the access area of the plant to indicate the presence of H2S. The alarm level in the plant area is set at 10ppm. Catalyst handling: at loading or unloading catalyst, wearing of masks is recommended to prevent inhalation of catalyst dust.
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL Portable H2S sensors are available as individual protection. • IMPORTANT • the employees should know the location of emergency equipment and how to use it; • the employees MUST understand the Dangers of exposure.
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL H2S AND SO2 DANGEROUS GASES H2S LOWER AND UPPER FLAMMABILITY LIMITS IN AIR ARE 4.3 and 45.5% by vol. IN STOICHIOMETRIC RATIO WITH AIR H2S IS VIOLENTLY EXPLOSIVE IF IGNITED All sources of ignition, open flames, sparks, (including static discharges), MUST be avoided H2S is a flammable gas burning in air to form sulfur dioxide and water with the liberation of heat. TOXIC BE CAREFUL WHEN DRAINING ACID CONDENSATE AND TAKING GAS SAMPLES
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL H2S AND SO2 DANGEROUS GASES Hydrogen sulfide is a colourless gas with a very unpleasant (=offensive odour) and characteristic smell (=rotten eggs). After prolonged exposure, the sense of smell will be lost (nose= No detection for workmen’s exposure!!!) Hydrogen sulfide at concentrations between 400 and 700 ppm is highly toxic and can cause immediate death at concentrations higher than 700ppm. Since the most parts of process streams have H2S content greater than 10.000 ppm, the unit must be completely gas tight and leaks repaired immediately they occur. It can be lethal to under-estimate an H2S leak.
PRECAUTIONS AND OPERATIONAL HAZARDS - GENERAL H2S AND SO2 DANGEROUS GASES Sulfur dioxide is a colorless gas, non flammable, with a suffocating odour: it’s toxic and corrosive. In the presence of mist or water this gas forms sulfurous acid and further sulfuric acid. Operators must be introduced to avoid inhalation of gas whenever possible, by working on the windward side of the place where gas is escaping. Sulfur dioxide causes irritation, dryness, infiammation of the breathing (=pain in the nose, throat,..)
PROTECTION OF THE PLANT PRECAUTIONARY MEASURES TO AVOID GAS EXPLOSIONS During an extended shutdown, all fuel gas and acid gas lines should be spaded at the battery limit. Before starting burners lighting trials, it is recommended that the area around the plant be tested with a flammable gas detector. Before attempting to light or re-light the fuel gas burners at the Thermal Reactor, or at the Incinerator, they must be well purged. The Thermal Reactor is purged with air at cold start-ups and with nitrogen at hot start-ups when sulfur is present in the unit. The Incinerator is purged with air by natural circulation.
LIQUID SULPHUR PROTECTION OF THE PLANT PRECAUTIONARY MEASURES TO AVOID SULFUR BURNING Sulfur burns exothermically with oxygen; uncontrollable sulfur fire can destroy the catalyst and damage vessels, refractory materials and pipework either for the resulting high temperatures or for the corrosive atmosphere due to the formation of SO3 during the sulfur combustion. Therefore whenever sulfur is present in the unit, care must be taken to limit its contact with oxygen. Sulfur burns with blue flame, which is difficult to see in daylight, then sulfur burning proceeds and evolves large quantities of SO2. During the plant heat up steps, in case of presence of liquid sulfur and when operating with fuel gas, the fuel gas must be burnt stoichiometrically. The process equipment and pipework must not be opened to the atmosphere until the sulfur is completely removed and the catalyst in the Claus reactors is cooled below 150 °C. AUTO IGNITION IN CONTACT WITH AIR AT TEMPERATURE HIGHER THAN 150°C
PROTECTION OF THE PLANT PRECAUTIONARY MEASURES TO AVOID SULFUR SOLIDIFICATION All the parts of the plant in which there is a flow of process gas and the possibility of liquid sulfur presence must be heated to the minimum temperature of 121 °C (because 115°C is sulfur solidifying temperature). Before starting the acid gas combustion and when some sulfur is present in the plant, the pressure of the steam produced in Waste Heat Boilers and Sulfur Condensers has to be higher than 1.1 bar (g) (which corresponds to a steam temperature of about 121 °C). The Claus catalyst bed temperatures throughout the reactors must be 15÷20 °C higher than the sulfur dew point temperature; if sulfur deposits are present on the catalyst, the catalyst can be temporarily deactivated and, in consequence, the sulfur recovery decreases. In such a case the inlet gas temperature in the reactors must be increased to sweep out the liquid sulfur.
PROTECTION OF THE PLANT PRECAUTIONARY MEASURES TO AVOID damage to CLAUS catalysts During the unit heating-up, frequent analysis of the flue gas are carried out to check that O2 and CO are within the following limits: O2 0.4 % by volume max. CO 0.4 % by volume max. Carbon formation can occur during the unit heating up if the fuel gas is burnt with oxygen deficiency: the carbon formed is filtered by the catalyst and poisons it permanently; additionally, the presence of carbon on the catalyst bed causes the poisoning of the liquid sulfur produced. The presence of a high quantity of oxygen in the process gas fed to the catalyst (more than 0.4% by volume) may cause catalyst sulfation, due to the formation of aluminium sulfate. This shall cause the decrease of the catalyst activity.
PROTECTION OF THE PLANT PRECAUTIONARY MEASURES TO AVOID damage to TGT hydrogenation catalyst During the normal operation the Claus tail gas should not contain oxygen. The oxygen presence shall be avoided in normal operation and during nitrogen circulation steps ,because the sulfided hydrogenation catalyst is subject to spontaneous combustion in the presence of oxygen. During the regeneration procedure (burn off sulfur and return the catalyst to its oxide state), high temperatures can be reached; special attention is required to perform this operation avoiding to thermally damage the catalyst (higher than 420°C).
PROTECTION OF THE PLANT PREVENTION OF DAMAGE TO REFRACTORY MATERIALS Thermal shocks of refractory materials can cause breakage. Working temperatures higher than normal may reduce the life of refractory materials. Presence of liquid water on the refractory material can cause disintegration. Therefore in case of presence of water on the refractory materials it is necessary to carry on a new refractory dry out before the plant restart up. During plant heating up, it is recommended that the temperature increase inside refractory lined equipment is limited
AT START-UP WITH FUEL GAS MONITOR THE OPERATION TO AVOID DAMAGE TO REFRACTORY LINING IN THERMAL REACTOR OR CATALYTIC BEDS. CARRY OUT FLUE GAS ANALYSIS TO CONTROL O2 AND CO CONTENT TO 0.4% AND 0.4% RESPECTIVELY MAXIMUM DURING FUEL GAS COMBUSTION FOR SWEEPING PLANT FROM SULPHUR. MODERATE TEMPERATURE WITH QUENCH STEAM. AVOID RUN‑AWAY TEMPERATURE IN CLAUS REACTORS. IF TEMPERATURE TENDS TO RISE UP TO 400°C DURING HOT STAND‑BY OR SHUT‑DOWN, CORRECT CONDITIONS FOR FUEL COMBUSTION HAVE TO BE RESTORED BY THE OPERATOR. ABOVE 155 °C VISCOSITY OF LIQUID SULPHUR WILL RISE RAPIDLY AND MAY HARM SULPHUR PUMPS. PRECAUTIONS AND OPERATIONAL HAZARDS – CLAUS SECTION
FUEL GAS COMBUSTION PRECAUTIONS AND OPERATIONAL HAZARDS – CLAUS SECTION • PAY ATTENTION TO: • FLAME TEMPERATURE IN THERMAL REACTOR • RUNAWAY TEMPERATURES OVER CATALYST BEDS • EXCESS AIR • BYPASS TGT SECTION • Check burners for flame quality • Observe refractory colour from burner sight glasses • Schedule frequency of sampling and analyses
AVOID ABSOLUTELY THE CONTACT BETWEEN THE CATALYST AND FREE OXYGEN EITHER DURING NORMAL OPERATION OR WHEN SHUTDOWN IN A SULPHIDED CONDITION. IN CASE THE CIRCULATING WATER pH CANNOT BE CONTROLLED, IT IS PREFERIBLE TO SHUTDOWN THE TGT SECTION, IN ORDER TO AVOID RISK OF SO2 ESCAPING IN THE TGT ABSORBER. LEAN SOLUTION HAS TO BE MANTAINED AT 40 °C MAXIMUM, IN ORDER TO MAXIMISE THE H2S ABSORPTION. BYPASS THE TGT SECTION TO PROTECT THE CATALYST DURING START‑UP AND UPSET CONDITIONS OF CLAUS SECTION. TGT SHUT‑DOWN IS NOT REQUIRED IF RECYCLE BLOWER IS STARTED AND A CIRCULATION OF INERT GAS IS KEPT. PRECAUTIONS AND OPERATIONAL HAZARDS – TGT SECTION
LEAN SOLUTION HAS TO BE MANTAINED AT 55 °C MAXIMUM, IN ORDER TO MAXIMISE THE H2S ABSORPTION. VISUAL INSPECTION OF AMINE SOLUTION TO CHECK THE COLOUR (THE BROWN IS DUE TO OXIDATION) AND THE PRESENCE OF SUSPENSION (IF BLACK INDICATES FERROUS SULPHIDE, IF AMBER INDICATES IRON OXIDES). VISUAL INSPECTION OF SOUR WATER TO CHECK THE PRESENCE OF SUSPENSION (IF BLACK INDICATES FERROUS SULPHIDE) OR THE PRESENCE OF HYDROCARBONS (OIL SLICKS). PRECAUTIONS AND OPERATIONAL HAZARDS – ARU/SWS SECTIONS
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