(47cn) Consequences Analysis Associated with the Failure of the Safety Interlock System of Methanator (I-351) of the Ammonia Plant of Fertilizantes Nitrogenados De Venezuela, C.E.C. (FertiNitro)

Consequences Analysis associated with the failure of the safety interlock system of methanator (I-351) of the Ammonia Plant of Fertilizantes Nitrogenados de Venezuela, C.E.C. (FertiNitro).

Fertilizantes Nitrogenados de Venezuela, C.E.C. (FertiNitro) is a petrochemical company, dedicated to the production and sale of anhydrous ammonia and granular urea high quality, located within the Oil and Petrochemical Complex General José Antonio Anzoategui, in the town of José, north of the Anzoategui state, adjacent to National Highway José Antonio Anzoategui (troncal 9), between Barcelona and Puerto Píritu Population. 30% of the production of these fertilizers are for the domestic market and 70% is exported to the international commercial market.

Throughout the value chain of Fertinitro, ammonia and urea are produced by transforming raw materials such as natural gas (which comes from the gas extraction plant of PDVSA) and atmospheric air. Fertinitro is formed by two identical trains, which in turn are cut by two anhydrous ammonia plants whose maximum production capacity is 1,800 tons per day each, and two granular urea plants, with maximum production capacity of 2,200 tons per day each. To achieve optimum performance of such plants, they are fed by the Industrial Services Unit and then the final product is sent to the storage unit and dispatch for further marketing.

Ammonia plant is divided into several sections (Desulfurization, Reformation, conversion, carbon dioxide removal, methanation, Synthesis Gas Compression, Synthesis and Ammonia Refrigeration). In the methanation section, the reactor is also known as methanator reactor (12/22-R-301), which introduces the process gas coming from the sections of Conversion and Carbon Dioxide Removal respectively (rich in hydrogen and Nitrogen with small traces of carbon monoxide and carbon dioxide).

Considering that the presence of carbon monoxide (CO) and carbon dioxide (CO₂) into the reactor 12/22-R-501 (located upstream of methanation section) produce adverse effects design intention inside thereof, the catalyst content in the methanator promotes an exothermic reaction converting the traces of CO and CO₂ to methane (CH₄). The resultant process gas methanation section contains primarily hydrogen (H₂), Nitrogen (N₂) with trace amounts of methane (CH₄) and argon (Ar), the latter two being inert in the ammonia synthesis section.

The inlet temperature to the methanation reactor is controlled by the Temperature Indicator Controller 12/22-TIC-3353 that, in split-range, the first controls the "by pass" associated with the exchanger gas / gas 12/22-E-311 A / B generating the opening of the temperatura control valve 12/22-TV-3353ª, and if is necessary additional heating, the 12/22-TIC-3353 sends a signal for the opening of the valve 12/22-TV-3353B and therefore increases the amount of the converted gas that passes through the heater 12/22-E-211 of the methanation reactor.

On the other hand, the temperatures in the catalyst bed is measured at four different levels in order to monitor the temperature profile. If there is a pass of CO and / or CO2 in the methanator due to poor operation of the CO conversion section and / or CO2 removal section, the temperature rise through the methanator may be so high that exceed the design temperature of the methanator. To avoid such an incident, it has been installed in the catalyst bed a high temperature switch to trigger the safety interlock system of the methanator (I-351). If the I-351 is triggered, the flow of process gas that is directed to the methanator is cut, being automatically vented downstream of the CO2 absorber (belonging to the CO2 removal section) through 12/22-PV- 3350 and downstream of the CO converter of low temperature through 12/22-PV-2076 12/22-PV-2076 a and B.

The I-351 activates the manual air vent on the top of methanator, which also can be operated safely from the control room. This action allows the gas to be vented through reverse flow of the methanator to protect the vessel and the catalyst from overheating during the release. When the I-351 is activated, the 12/22-HY-3050 decrease the pressure at 2 kg/cm2g per minute, opening the 12/22-HV-3050.

In that sense, due to hazardous materials that are handled in this equipment, plus the operating conditions, it is considered a high-risk equipment, that is why there is a need to realise an consequences analysis associated with the failure of the safety interlock system of methanator (I-351) of the Ammonia Plant of Fertilizantes Nitrogenados de Venezuela, C.E.C. (FertiNitro).