Fired heaters length

Reaction condition optimization considers reaction severity in terms of temperature and pressure profiles in accordance with catalyst performance in the entire run length. Optimizing reaction conditions, selecting better catalysts, and maintaining catalyst performance in operation have significant effects on both yields and energy efficiency. Consider reaction temperature as an example. In the catalyst cycle, the catalyst performance deteriorates, which affects the reaction conversion. To compensate, the reaction temperature may be increased. However, more severe reaction conditions require more heat from hot utilities such as fired heaters, while severe conditions also produce more desirable products as well as undesirable by-products. The question is how to determine the optimal reaction temperature, which is a function of reaction conversion, production rate, and energy use. 

The nonuniformity of heat flux around mbe is described by the circumferential flux factor, which is the ratio of peak flux to average flux. Peak flux determines the maximum TWT. The peak flux is typically 1.5-1.8 times the average for a single-fired heater, while it is 1.2 times the average for a double-fired heater. That explains why the double-fired heater has longer run length as it has lower flux rate and hence lower TWT than the single-fired heater. 

Operators understand the importance of maintaining fired heaters in a safe and rehable condition. The response from operators to this priority could go to another extreme run fired heaters with too much excess air. The result of much excess air is much reduced flame length and thus the risk of flame impingement is minimized. 

Honzontal-tube cabin heaters position the tubes of the radiant-section-coil horizontally along the walls and the slanting roof for the length of the cabin-shaped enclosure. The convection tube bank is placed horizontally above the combustion chamber. It may be fired From the floor, the side walls, or the end walls. As in the case of its vertical cylindrical counterpart, its economical design and high efficiency make it the most popular horizontal-tube heater. Duties are 11 to 105 GJ/h (10 to 100 10 Btu). 

In order to adequately describe the size of a heater, the heat duty, the size of the fire tubes, the coil diameters and wall thicknesses, and the cor lengths must be specified. To determine the heat duty required, the maximum amounts of gas, water, and oil or condensate expected in the heater and the pressures and temperatures of the heater inlet and outlet must be known. Since the purpose of the heater is to prevent hydrates from forming downstream of the heater, the outlet temperature will depend on the hydrate formation temperature of the gas. The coil size of a heater depeiuLs on the volume of fluid flowing through the coil and the required heat duty. 

Fire uihe area required and heater size (shell diameter, shell length, fire luhe rating, coil length and number of passes). 

With hot water units, time clock control can operate satisfactorily as automatic bypass valves built into the distribution system will help the heater to achieve its working temperature quickly. With steam boilers, it is important that the boiler reaches a reasonable working pressure before steam is allowed into the distribution system. For example, if boilers are left open to a system for an extended length of time while not firing they will quickly lose their pressure. This is not only wasteful of energy but eventually creates a problem on start-up. To... 

Double-fired, multi-point steam (or water) injection, online spalling, bi-direction steam/air decoking and other techniques enable a three-year run length for the heater and 5% savings. 

For the purpose of this article, fire tests are associated with the second strategy and defined as experimental methods to characterize the behavior of polymers under more severe thermal exposure conditions that are representative of the growth phase of a compartment fire. These conditions are simulated with a gas-fired or electrical heater or a large gas burner turbulent diffusion flame (flame length of the order of a meter or several feet). The incident heat flux to the specimen is primarily radiative when heaters are used, and mainly convective for flame exposure. Total incident heat flux varies from approximately 1 kW/m to more than 100 kW/m. Note that the maximum radiant heat flux from the sim on earth is approximately 1 kW/m. Polymers that are not treated with fire retardant chemicals typically ignite when exposed to heat fluxes of 10-20 kW/m in the presence of a small pilot flame or hot spark. 

A barrel of 12°API resid takes perhaps 10% more furnace duty than a barrel of 8°API resid for identical heater inlet and outlet temperatures. Thus, a heater maintaining a constant outlet temperature will start firing much harder when it receives a slug of light feed. If overfiring results, the heater run length will be abbreviated. 

Why do operators often run with too much air and hence waste energy For one thing the flame temperature is reduced. Also, more excess air produces more flue gas. This increases heat pickup in the convective section. Finally, flame length is shortened and flame impingement is reduced. These factors make it easier to fire the heater without overheating the tubes. Unfortunately, the price must be paid in lost furnace efficiency and wasted energy. 

Newer heaters typically have thin reflective tiles, rather than massive refractory brick walls. Such newer heaters will heat up more rapidly. Also, the process fluid outlet temperature responds more rapidly to changes in the firing rate. This improves the heater outlet temperature control. Perhaps for this reason, it seems that heaters with reflective refractory walls are less subject to process tube coking and shortened heater run lengths. There is also a process, called "alonizing," that increases the reflectivity of older brick refractory heater walls. 

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