Fired heaters passes

Fired heater pass balancing is often installed to equalise pass temperatures in order to improve efficiency. Chapter 10 shows that the fuel saving is negligible and that, in some cases, the balancing may accelerate coking. However there may be much larger benefits available from the potential to debottleneck the heater. 

Reducing gas is generated from natural gas in a conventional steam reformer. The natural gas is preheated, desulfurized, mixed with steam, further heated, and reformed in catalyst-filled reformer tubes at 760°C. The reformed gas is cooled to 350°C in a waste heat boiler, passed through a shift converter to increase the content, mixed with clean recycled top gas, heated to 830°C in an indirect-fired heater, then injected into reactor 4. 

NO -laden fumes are preheated by effluent from the catalyst vessel in the feed/effluent heat exchanger and then heated by a gas- or oil-fired heater to over 600° F. A controlled quantity of ammonia is injected into the gas stream before it is passed through a metal oxide, zeolite, or promoted zeolite catalyst bed. The NO is reduced to nitrogen and water in the presence or ammonia in accordance with the following exothermic reactions ... 

A typical process flow diagram of a catalytic reformer is shown in Figure 3.17. Desulfurized naphtha is heated in feed-effluent exchangers and then passed to a fired heater, where it is heated to 850 to 1,000° F (455 to 540° C) at 500 psia (3,450 kPa) in a series of reactors and fired heaters. In the reactors, the hydrocarbon and hydrogen are passed over a catalyst (often platinum/rhenium based) to produce rearranged molecules, which are primarily aromatics with some isoparaffins. The reactor effluent is cooled by exchange and then passed to a separator vessel. The gas from the separator is recycled to the reactors. The liquid is fed to a fractionator. 

Description The Isomar process re-establishes an equilibrium distribution of xylene isomers, essentially creating additional paraxylene from the remaining ortho- and meta-xylenes. The feed typically contains less than 1 wt% of paraxylene and is first combined with hydrogen-rich recycle gas and makeup gas. The combined feed is then preheated by an exchanger (1) with reactor effluent, heated in a fired heater (2) and raised to the reactor operating temperature. The hot feed vapor is then sent to the reactor (3), where it is passed radially through a fixed-bed catalyst. 

This technology has been used extensively for the production of butadiene and, in more reeent years, for that of isobutylene and propylene.The feed is preheated through a fired heater before being passed over the eatalyst in the reactors. The hot reactor effluent is eooled, eompressed, and sent to the produet... 

When the process is purge-gas limited, direct heating should be the method of choice. Direct heating is accomplish external to the adsoiber vessel by passing the puige gas through a heat exchanger or fired heater, lliis is much simpler, offers better temperature control, and results in a more unifoim heathy of the adsoibent. 

This example is provided for illustrative purposes only. It uses a fired heater low-pass flow SIF to illustrate various technical points. The design is not intended for use in any real application. The reader should review relevant application specific standards and technical reports to ensure that the process hazards are identified and that the design is complete. 

The fuel gas to a fired heater is controlled by a BPCS control function (function TIC-1), which throttles a fuel control valve, CV-1, as shown in Figure F-3. A hazard analysis was performed to identify process hazards and to determine whether the safeguards were sufficient to mitigate the process hazards. The team determined that when the heater was firing hard, a low-pass flow through the tubes could result in a high firebox temperature with the potential for tube rupture, furnace fire and structural damage to the furnace. 

Fire-tube heaters—furnaces consisting of a battery of tubes that pass through a firebox. Fired heaters or furnaces are commercially used to heat large volumes of crude oil or hydrocarbons. Basic designs include cylindrical, cabin, and box. 

A furnace, or fired heater, is a device used to heat up chemicals or chemical mixtures. Furnaces consist essentially of a battery of fluid-filled tubes that pass through a heated oven. These devices provide a critical function in the daily operation of the chemical processing industry. Process heaters are more technically defined as combustion devices designed to transfer convective and radiant heat energy to chemicals or chemical mixtures. These heaters are typically associated with reactors or distillation systems. Process heaters come in a wide variety of shapes and designs, but the basic styles include cabin, box, and cylindrical. The various parts of a process heater include a radiant section and burners, a bridgewall section, a convection section and shock bank, and a stack with damper control. Modern control instrumentation is used to maintain these rather large and elaborate systems. 

Operating with a control valve bypass open is not permitted by many operating companies. In theory, I agree that control valve bypasses should be kept closed. In practice, I frequently have opened bypasses. For example, we have a fired heater that is limited by the unit charge pump. Opening the bypasses around the heater pass control valves seems reasonable and safe. But suppose there is a leak in a heater tube. The panel operator closes the pass control valve remotely to stop the fire, but the flow continues through the bypass valve. The reader can imagine how I became so smart on this subject. 

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