Revamps 2023 Issue

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 pri - marily 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 hydro - carbons into aromatics. This transformation yields high-oc - tane 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 tem - peratures of the reactants must be elevated beyond 500°C, usually 520-540°C for catalytic reformers. This temper - ature 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 dou - ble 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. Pre-application conditions Before the project, the refinery had searched for a solution to gain efficiency of its catalytic reformer unit and prevent any radiant tube oxidation. This oxidation scale acts as a strong barrier for heat transfer and may decrease radiant coil thermal conductivity. In the case of no scale formed on the surfaces, it has been calculated that there is a potential gain on radiant efficiency of at least 11.2 % from the initial state throughout the run. It is worth mentioning that the feed naphthene content, which has a direct effect on the BWT limit, was expected to increase by an additional 5 to 10 vol.%. It allows a wider operational flexibility for the feed selec - tion choice. Application

Figure 1 ISO SA 3 sandblasted tubes

High emissivity tube and refractory coatings for catalytic reforming units Since, in most cases, tubes in catalytic reforming fired heat - ers 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, eventu - ally leading to a BWT limitation and reduced production rate. High emissivity tube coatings can provide the follow - ing 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 endothermic. To initiate these reactions, the inlet temperatures of the reactants must be elevated beyond 500°C, usually 520-540°C for catalytic reformers The dehydrogenation reactions within these processes are

High emissivity coatings were applied to all radiant surfaces in all three heat - ers during a major turnaround. A spe - cial ceramic coating system has been selected for each type of surface. As a first step, tube surfaces have been prepared to meet ISO SA 3 standards (SSPC-SP5, NACE No. 1) via blasting to white metal conditions (see Figure 1 ). During tube blasting, the refractory was protected with tarps to prevent damage. After the blowdown of the unit

Figure 2 Tubes (on the left) and refractory (on the right) after coating

Revamps 2023