Refinery strikes liquid gold with efficiency increases in catalytic reformer

Refinery strikes liquid gold with efficiency increases in catalytic reformer
Published: 21 August 2019 - 10 a.m.
By: Indrajit Sen
Catalytic reforming converts low-octane, straight-run naphtha fractions, particularly heavy naphtha, into a high-octane, low-sulphur reformate, which is a major blending product for gasoline/petrol.

The process is endothermic and is carried out by feeding a naphtha and hydrogen mixture to a furnace, where it is heated in a series of fired heaters to the desired temperature, 450°C to 520°C (840°F to 965°F), before passing through a series of reactors.

Thermal inefficiencies
In a high-temperature environment, steel alloy process tubes will immediately oxidise, and scale will develop. This oxidation scale layer acts as an insulator and will lead to a decrease in heat transfer as the scale increases in thickness. To compensate for the insulating effect of the scale, the heater is subjected to excessive fuel firing.

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Simulated view: Typical process tube condition.

The resulting increased temperate promotes the development of further scale. As oxidation continues, tube metal is consumed leading to a decrease in tube wall thickness, which shortens the tube life.

Ceramic coatings
Ceramic coatings for process tubes prevent oxidation and scale formation for approximately two turnarounds. This thin-film coating maintains the process tube in a like-new condition, maximising conductive heat transfer to the process and increasing radiant section efficiency. Likewise, by stopping oxidation, tube metal loss is prevented.

Coating refractory lining
The emissivity of typical refractory linings in fired heaters ranges from 0.45-0.65. When radiant energy encounters these refractory linings, much of the energy is reflected back and is absorbed into the flue gas and carried out of the radiant section, into the convection section and out the stack, with the majority never reaching the process.

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Simulated view: Process tubes under IR illustration.

High emissivity coatings for refractory surfaces increase surface emissivity to 0.92, a near black body. Radiant energy is absorbed by the high emissivity lining and reradiated across a broad spectrum. The reradiated energy is able to penetrate the flue gas and be absorbed by the process increasing radiant section efficiency.

Heater evaluation at a refinery
A refinery reported that excessive process tube scale on their catalytic reformers was creating a limitation and contacted Cetek, a global turnkey provider of ceramic high-emissivity coatings and a division of Integrated Global Services, for an inspection and recommendation. Cetek visited the site to conduct an infrared inspection of the heaters. After reviewing the infrared images and the data supplied by the refinery’s process engineer, Cetek’s fired heater expert recommended both high-emissivity coatings for process tubes and refractory surfaces for all heater cells. The results of this evaluation are summarised below:
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Benefit category Benefit percentage
Radiant section efficiency 7.0%
CO2 emission reduction 6.5%
NOx emission reduction ~10%

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Simulated view: Side-by-side comparison of process tubes with and without ceramic coating.

With the predicted fuel savings and capacity increase from the application of high emissivity ceramic coatings, a payback period and return on investment was calculated over the life of the coating. Keeping the same production rate, the coating would produce over $2.9mn in fuel savings; when keeping the same firing rate and increasing throughput, over $10.5mn in additional profit could be realised from the increase in production.

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Before the application of Cetek coating.

Post application report
After the coating was applied and the catalytic reformer was returned to service, and conditions in the heaters were similar to the pre-evaluation conditions, a fired heater study was completed to measure the actual benefits of the ceramic coatings. The increase radiant efficiency of 10% was achieved.

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After the application of Cetek coating.

Taking the cost of the project and the benefits into consideration, the payback was 14 months in terms of fuel savings, or four months for capacity rate, or process severity increase.

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