“RUMBO A LA TIERRA PROMETIDA CON TRES CLASES DE CREYENTES.”

TECHNOLOGY : Technip,France CAPACITY : 65000 MTPA INTRODUCTION :

A New Hydrogen Generation Unit of 65000 metric tones per annum of Hydrogen producing is recently included in the secondary processing facilities. The primary objective of the Hydrogen Generation Unit is to produce hydrogen to meet the entire hydrogen requirement of Hydrocracker,Diesel Hydro Desulphurization Unit,Diesel Hydrotreatment Unit & the new upcoming project Motor Spirit Quality Upgradation Unit.

PROCESS DESCRIPTION :

1. FEED PRE-DESULPHURIZATION :

The feed contains unsaturated components as well as high amount of organic sulphur. Sulphur would act as a poison for the downstream process catalysts and needs to be removed. The bulk of the sulphur can be removed by conversion (hydrogenation) of the organic sulphur components to H2S and subsequent stripping.The feed to the unit is the straight run naptha which is passed through filters & collected in the sour naptha feed surge drum.The feed is mixed with hydrogen recycled from PSA & fed into the furnace through a series of heat exchangers.The temperature of the mixture is raised to 310-330 oC so the naptha gets vaporized.The superheated sour naphtha / H2 mixture is fed to the

hydrogenation reactor which consists of two layers of catalysts, with the top layer consisting of Nickel Molybdenum and the bottom layer consisting of Cobalt Molybdenum catalyst. In this reactor, the olefinic compounds in the feed naphtha get saturated and the sulphur in the naphtha gets converted to H2S. The chlorine present in the feed gets converted to HCI.The mixture coming from the reactor is cooled in heat exchangers & water coolers & sent to a separator having a pressure of 19 kg/cm2.The liquid naptha from the separator drum contains dissolved H2S is heated to 125 oC & sent in the stripper where the H2S is stripped off & naptha is taken as the bottom product.

 RSH + H2  RH + H2S

 RCI + H2  RH + HCI

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2. FEED DESULPHURIZATION :

The sweet naphtha, collected in the sweet naphtha surge drum. This naphtha is pumped by the sweet naphtha feed pumps to a pressure of approximately 39 kg/cm2g.The feedstock is mixed with hydrogen under ratio control and preheated to about 120C in the heat recovery section.This feed is vapourized by HT shift effluent in the feed naphtha vaporizer and is superheated to about 380 C to 400 C in the convection coil.

This is now fed to the hydrogenation reactor to convert any residual organic sulphur to H2S.This reactor contains 4.5 m3

of CoMOx or any other equivalent catalyst.The recycle hydrogen is mixed to provide a mole ratio of 0.25 to provide the necessary amount of hydrogen for conversion of sulphur in the hydrogenation reactor.The hydrogenated feedstock is then passed through the feed desulphurizers A/B containing the chlorine guard and zinc oxide catalyst.Reactor A consists of a bed of 4.1 m3 of Chlorine guard Al2O3 followed by reactor B having 2.2 m3 of ZnO.H2S & HCl are absorbed according to the reactions given below.

Hydrogenation reactor :  RSH + H2  RH + H2S Reactor A :  Al2O3 + 6HCI  2AlCl3 + 3H2O Reactor B :  ZnO + H2S  ZnS + H2O 3. PREREFORMER :

The desulphurized feed is mixed with a controlled quantity of steam based on the calculated hydrocarbon weight flow and the required steam to feed ratio. There are two prereformers, one in operation and the second on standby. Each reformer is designed for a life of 12 months operation and consists of 5.9 m3 of Katalco 65-3R (Ni based catalyst). After heating to required temperature of 460C in the pre-reformer preheat coil 3, the gas is passed through the prereformer A/B which is operated adiabatically and will convert the naphtha to methane, carbon dioxide, carbon monoxide and hydrogen.This results in a feed, which can be further preheated to minimize the reformer duty. The steam to feed ratio varies from 3.0 to 2.4 to enable additional temperature control for inlet to the prereformer.The feed in the presence of steam reacts to a mixture of methane, carbon dioxide, carbon monoxide and hydrogen over a nickel based catalyst. These reactions take place in both the pre-reformer as well as the reformer. The principle reactions are:

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 CnHm + nH2O  nCO + (½m + n) H2 - Heat

 CO + H2O  CO2 + H2 + Heat

The CO formed from these higher hydrocarbons will be partly converted to methane. For n=1 and m=4; this reaction is referred to as the ‘steam methane reforming reaction’, the reverse reaction is generally referred to as ‘ methanation reaction. The reversible conversion of methane with steam to CO and hydrogen is strongly favoured by a high temperature, low pressure and high steam quantity which is maintained in the reformer.

4. REFORMER :

In order to achieve a higher hydrogen yield from the feedstock, after the prereformer the methane is further converted in the reformer, which operates at a higher temperature.The reaction in the reformer is strongly endothermic so burners are provided in the reformer.Before superheating in the mixed preheat coil , additional steam is added to meet the required steam to carbon for the steam methane reformer which consists of 204 tubes, 12.2 m heated length arranged in 6 lanes each of 34 tubes. Each tube is filled with Katalco 25-4 and Katalco 57-4(Ni based catalyst) in the ratio of 40% : 60% of the heated tube length.The reformer is designed to operate at a steam to carbon of 2.75 mol/mol, which is achieved, by an overall steam to feed of 3.25 kg/kg.The steam to carbon ratio will be increased at lower capacities.The normal reformer inlet temperature is around 650 - 665 at 10. The gas is distributed over the reformer tubes where the reforming reactions take place and an outlet temperature of 880 - 885C is reached.Coking is prevented using excess of steam.

5. SHIFT REACTOR :

The gas mixture, which leaves the reformer, is essentially at equilibrium of the shift reaction. Since the equilibrium of the reaction shifts with the temperature, shift conversion will be applied at comparatively lower temperatures to further convert carbon monoxide to hydrogen. There are two temperature levels at which the reactors are operated. The first stage reactor is the High Temperature Shift Reactor and the other, Low Temperature Shift Reactor. The principle reaction is

 CO + H2  CO2 + H2

Reactor inlet temperature of 327C fo. In order to increase the hydrogen content in the syngas from the reformer, the bulk of the carbon monoxide is converted by steam to hydrogen and carbon dioxide in the high temperature shift reactor 302-R-14 filled with 25.6 m3 of Katalco 71-5 catalyst. The reformer effluent is cooled to the required inlet temperature for the high temperature shift reactor in the process gas boiler.The effluent from the HT Shift Reactor is at a high temperature. After sufficient heat recovery the effluent is sent to the 2nd shift reactor for more hydrogen

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6. HYDROGEN PURIFICATION :

In the Pressure Swing Adsorbtion Unit, the hydrogen is hydrogen leaving with a purity of more than 99.99 vol% and the rest of the process gas is purge gas and serves as primary fuel for the reformer. PSA technology is used to remove the impurities from the reformed gas. This is achieved by molecular sieves, which adsorb the contaminants at high pressure and allow the hydrogen to pass. To regenerate the molecular sieves the adsorber is depressurized. This releases the contaminants and after pressurization the adsorber is ready for reuse. The contaminants, which are released at low pressure, are collected in the purge gas drum and are used to meet part of the heat demand of the reformer. There are 12 vessels containing the adsorbent, out of which three are used for adsorbtion, others are used for desorption & maintaining the pressure. This is a automatic process each vessel having a cycle of 60 seconds.

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