Oct-2023

Increasing efficiency of catalytic reformer unit fired heaters

Application of ceramic coating on CRU heater tubing and refractory avoids oxidative scale formation, significantly lowering fuel consumption and CO2 formation.

Diyar Kiliç Mert and Alp Zeren, Tüpraş Izmit Refinery
Anton Korobeynikov and Sergei Merchev, Integrated Global Services (IGS)

Article Summary

Catalytic reforming units (CRUs) are one of the highest margin but most energy-demanding processes in oil refining. This flexible technology can produce high-octane gasoline components and individual aromatic hydrocarbons (xylene, benzene, toluene), which are raw materials for the petrochemical industry. The reforming process involves converting low-octane naphtha into a reformate at high temperatures and relatively low pressure.

Catalytic reforming is typically carried out in a series of four reactors. Before entering each reactor, the feedstock is reheated to a temperature of 520-540°C. This reheating is achieved using high heat flux fired heaters consuming sizeable amounts of energy and emitting greenhouse gases (GHGs).

Radiant coils within the catalytic reforming fired heater are made of 9%Cr chromium/molybdenum alloy (ASTM A335P9) and are subject to oxidation scale formation under firebox conditions. This oxidation scale may reach up to 1-2 mm thicknesses, reducing radiant coil thermal conductivity, hindering radiant section efficiency, and significantly impacting the entire plant’s economic performance.

Enhancing radiant efficiency
A CRU with continuous catalyst regeneration (CCR) experiences a high rate of scale formation, approximately reaching metal loss levels of 0.15-0.25 mm/year. The plant team thoroughly tracked the performance and detected an energy efficiency decrease due to scale formation. Every four years, during a major turnaround, the plant carried out activities to clean the external tube surfaces. Nevertheless, a significant decrease in furnace efficiency was observed by the end of the second year after the turnaround.

A detailed analysis of furnace operational data revealed the feasibility of high-emissivity ceramic coatings application to the radiant tube and refractory surfaces. The project was executed during a major turnaround, and the furnace performance analysis was carried out two months later. Post-project analysis showed a radiant efficiency gain of 13%, expected to last over the coating’s service life (8-10 years). Achieved radiant efficiency enhancement may be utilised for reducing fuel consumption along with CO2 emissions or throughput/severity increase under the same firing rate.
Scale formation

Refineries seek ways to find energy optimisation solutions in their processes and prioritises projects that are geared towards reducing fuel gas consumption and cutting GHG emissions. These initiatives align with strong commitments to a zero-carbon strategy, sustainability, and optimised energy usage, especially for units like the catalytic platformer.

While platforming reactions occur in the stacked set of reactors, scale formation is observed on the external tube heater’s surfaces due to oxidation, fuel gas impurities, and high heat flux. Oxidation scale formation results in the non-uniform heat distribution along the tubes and hotspots formation. Moreover, the radiant efficiency of the heater decreases with the corresponding fuel consumption increase. To prevent oxidation scale formation, the refinery decided to apply ceramic coatings to the furnace tube and refractory surfaces on-site during a turnaround.

This case study pertains to the application of Cetek High Emissivity Coatings on both radiant tubes and refractory surfaces within the refinery catalytic reforming heaters. The primary objective was to enhance radiant efficiency and facilitate the sustainable operation of the heater for the next 8-10 years.

Ceramic coatings nowadays are approved materials to increase the energy efficiency of fired heaters or debottleneck the heaters with various limitations, such as bridgewall temperature (BWT), firing duty or uneven heat flux distribution. Initially developed in the 1970s, coatings have found successful use in all heavy industrial applications, including metals processing, aerospace, glass industry, and fertilisers but became especially beneficial in the oil and gas and petrochemical industries.
High emissivity tube and refractory coatings for catalytic reforming units

Since, in most cases, tubes in catalytic reforming fired heaters are made of 9%Cr steel, they experience oxidation scale formation on the external surfaces. Heavy scale creates poor conductive heat transfer through the tube wall to the process. This leads to over-firing and high BWTs, eventually leading to a BWT limitation and reduced production rate. High emissivity tube coatings can provide the following benefits:
• Reduce fuel consumption or increase capacity under the same firing
• Increase emissivity of tube surface up to 0.92
• Prevent oxidation scale formation
• Lower BWT and increase radiant efficiency
• Reduce CO2 and NOx emissions.

Additional benefits can be provided by high emissivity ceramic coatings applied to the refractory surfaces, which improve radiant heat transfer efficiency to the process over design conditions.

General heater information
Catalytic reforming units are initially designed to primarily generate a high-octane reformate. Nevertheless, in response to the increasing demand for hydrogen (H2), these units have gained additional significance as a key source of hydrogen for hydrotreating and hydrocracking processes. The reforming processes entail the conversion of lower- octane heavy naphtha, converting C7-C10 hydrocarbons into aromatics. This transformation yields high-octane reformate, hydrogen gas, and a minor proportion of liquefied petroleum gas (LPG).

The dehydrogenation reactions within these processes are endothermic. To initiate these reactions, the inlet temperatures of the reactants must be elevated beyond 500°C, usually 520-540°C for catalytic reformers. This temperature elevation is typically achieved using fired heaters chosen for their comparatively high efficiency compared to other alternatives. The substantial heat input requirements of these heaters also necessitate careful monitoring of the emissions they generate.

The catalytic reforming unit consists of four cells with sketches available in the public domain. All cells have double firing with burners located on the bottom. Tubes are made of A335P9 steel, and walls and arch are insulated with castable refractory. The internal division walls and floor are made of insulating firebrick.