Steam Reforming Catalyst Reduction with LPG Feed

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Steam Reforming Catalyst Reduction with LPG Feed

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Steam Reforming Catalyst Reduction with LPG Feed

Scope This procedure may be used for the reduction of VULCAN Series Catalysts for the general steam reforming of LPG. It is strongly advised that this procedure is adopted only where there is no other option available to use hydrogen, a hydrogen-rich gas or natural gas for the reduction stage. Reduction using the cracking of heavier hydrocarbons carries an extreme risk of catastrophic carbon formation in the event of any error in execution of the procedure. Introduction LPG is not normally utilized for steam reforming catalyst reduction although it can be used successfully. Caution is required if heavier hydrocarbons are used for catalyst reduction. Although operators have been able to reduce catalysts by using heavier hydrocarbon cracking, this has only been adopted where no other reductant option is available. The risk of carbon formation greatly increases as the carbon number of the feed increases when the catalyst is in the unreduced state. For the purposes of this procedure, LPG may range from a hydrocarbon mixture which is predominantly propane to one which is predominantly butane. Reduction Using LPG The probability of success is greatly enhanced by increasing the care taken during the reduction, over and above that used for hydrogen or natural gas reduction. The operator must be confident that both steam and hydrocarbon flow metering are properly calibrated and accurate during the reduction procedure as one of the prevalent causes of inadvertent carbon formation during this procedure arises from metering errors. It is therefore important that the flowmeters be span checked and if possible calibrated for the conditions that will be utilized during the catalyst reduction. All changes to feed rates and temperatures should be carried out with extreme care. When increasing feed rate, ensure that the steam rate is increased before the feed rate is increased. Conversely when reducing feed rate, ensure that the feed rate is reduced before the steam rate is reduced. Steam reformer operation must be extremely closely monitored including very frequent visual inspection of the furnace including tube appearance, flame stability and so forth.



1. Purge the plant free of oxygen using nitrogen, and heat the reformer above the condensation temperature while still circulating nitrogen. Steam may be added as soon as possible after the temperature of the exit header is at least 50°C above the condensation temperature of steam.

2. The steam flow should be increased to approximately 50% of the design

rate (commensurate with plant design constraints) as soon as possible to allow even firing of the furnace. During reduction of catalysts with LPG operation at the correct steam ratio is critical. With too high a steam to carbon ratio, the catalyst will not reduce whereas too low a steam to carbon ratio will lead to carbon formation. During reduction, it is usual to stay below design pressure to allow early introduction of steam without condensation and to protect the tubes by providing an additional margin against over temperature and hence failure. Therefore, the accuracy of the steam flow meter must be verified for operation at approximately 50% of design rate and this lower pressure operation. The use of a separate DP cell on the steam orifice calibrated for start-up conditions may be considered.

3. Nitrogen circulation may be stopped at any convenient time after steam

has been added and before LPG is introduced.

4. Increase the reformer exit temperature to 750°C at an appropriate rate dependent upon the allowable furnace heating rate. At all critical stages during reduction it must be emphasized that the temperatures referred to are those at the actual tube exit. Temperatures indicated by control room instruments are inevitably lower than the true value because heat losses. Allowance must be made for the discrepancy. Depending on the location of the thermocouples, indicated values may be 25 -100°C (45 – 180oF) lower than actual temperatures.

5. Introduce the LPG feedstock at about 5% design rate. This will result in

a steam:carbon ratio of approximately 30:1. Increase the LPG feed rate to 10% of design rate over a period of 1 hour. This will reduce the steam to carbon ratio to approximately 15:1. At the same time, increase the reformer exit temperature to the design level or 800oC (1472oF) whichever is achieved first. The heat requirement in the furnace will increase as the endothermic steam reforming reaction begins. As catalyst reduction proceeds, the furnace firing should be trimmed to maintain the necessary exit temperature.



The recycle hydrogen rate should be adjusted to give the recommended hydrogen concentration for acceptable hydrodesulfurization as soon as possible after feed has been introduced.

6. Since at start up the LPG flow is very low (5% - 10% of design) the

accuracy of the flow meter should be verified at this low flow. The use of a low range flow transmitter would decrease the risk of operating with too high an LPG flow and low steam to carbon ratio. It should be noted that when the LPG feedstock pumps are lined up and the discharge pressure raised there may be a small leakage of LPG past the isolation valves due to the high differential pressure. This may result in a reduction in the reformer exit temperature as reforming reactions take place. Small leaks are not likely to create carbon in the reformer due to the very small leakage rates experienced but more serious leaks introduce the possibility of severe carbon formation.

7. Increase the LPG feed rate to give a steam to carbon ratio of 7:1. At a

steam flow of ~50% of design and a steam to carbon ratio of 7:1 this corresponds to an LPG feed rate of approximately 20% of design.

8. During catalyst reduction, the tube inlet temperature should be as high

as possible to promote maximum reduction at the inlet of the tubes.

9. Hold the steam to carbon ratio at 7:1 for a period of approximately 12 hours, by which time the catalyst will be reduced. As the catalyst reduces more LPG will be reformed. During this stage, the exit methane and heavier hydrocarbons concentrations should be checked at hourly intervals. Reduction should be complete when the exit methane concentration reaches a low steady value and the presence of heavier hydrocarbon cannot be detected. At this point the reformer exit temperature can be decreased to the design exit temperature, if a higher temperature has been used to promote desulphurisation.

10. When the catalyst has been reduced, the LPG feedstock rate should be

increased slowly to the design steam ratio and flow rate. This should take about 2-3 hours. Check the methane concentration in the reformer exit gas after each change to ensure that it stays at a low steady value. If the methane or heavier hydrocarbon concentration increases or the tubes show hot zones, continue reduction for a further period at a steam to carbon ratio of 7:1, before once again increasing the LPG flow to the design steam to carbon ratio. When flow rates are being increased, it is always important to increase the steam flow before the feed flow in order to maintain the steam ratio at or above the design value.



11. If the catalyst has not been fully reduced, the tubes may appear to be

hot. However, the catalyst should reach its fully reduced state after approximately 24 hours normal operation. If this is not the case, it may be necessary to stop the feed and restore reducing conditions for a few hours.