OCR Text |
Show Process heaters are very predominant and conswne the most fuel in a complex refinery. Unit operations that use large process heaters include the majority of refinery operations. Feed, liquid or gaseous, is preheated against product gases and fmish heated in a process heater or furnace to temperatures between 200 and 1,600°F. Furnaces ~ay be t?P- or bottom-fired with a few large burners, or side wall-fued with a large array of small burners. Heat mputs WIll vary ~etween 20 and 500 MMBtuJhr. Burners may be natural draft or forced draft (sometimes with air preheat). The prmlary mode of furnace heat transfer is by radiation, with furnace flue gases exiting at as high as 1,80~°F. Do~ stream convective sections either preheat feed or a heat transfer fluid to improve unit thermal effiCIency. FlUIds heated vary widely in physical and chemical composition and are sometimes prone to cracking in the ~ace tubes because of uneven furnace wall heating. Air emissions include the acid gases (NOx and SOj, and air tOXICS. . Steam is generated in large water tube, direct-fired, packaged or field-erected boilers. Boilers are also so~et~es.fued or co-fired with refinery fuel gas, CO, or natural gas for purposes of thermal destruction. Air emIS~lOnS mclude acid gases and air toxics, and particulates smaller than 10 microns (PMI0). Boilers typically have heat mputs of 100 to 1,000 MMBtu/hr. Burners are forced draft, multi-fuel, frequently with combustion air preheat in their larger sizes. Large frame and aero-derivative gas turbines are now frequently found in large (> 100,000 Bbb/day) refineries and produce power sufficient for minimwn operation, typically 40 to 200 MW. Most are equipped with NOx control technologies including steanl or water injection, CO and NOx catalytic control, and more recently with dry, low NOx combustors. They typical1y burn a blend of refinery and natural gas. Turbine exhaust heat is recovered in heat recovery steam generators or specially designed process heaters. 4.1.2 Research Needs There are a nwnber of research needs identified in this evaluation. The greatest single focus was on research for improving the product or purpose of the combustion equipment. For example, research to improve heat transfer to the heated fluid in process heaters by enhancing flame radiation heat transfer was considered most important for process heaters and burners used in process heaters. Short-tenn (within 3 years) research was considered more important than longer-tenn research, because of the belief (especially in environmental concerns such as air emissions) that changing regulatory requirements make the longer term too uncertain. General types of combustion equipment technologies were suggested to the survey respondents as initial starting points from which to identify combustion needs. The survey respondents considered multiple burner arrays, catalytically assisted combustion, fluidized beds, mass bun1, suspended circulation, and porous media. Practically any research that focuses on the performance and air emissions, especially acid gases (primarily NOj and air toxics, for multiple burner arrays and catalytically assisted combustion is considered a high priority. Most process heaters are multiple burner arrays, and catalytically assisted processes such as catalytic cracking and reforming are very important refinery operations. However, there were several major research needs that were important not only for multiple burner arrays and catalytically assisted combustion, but were crosscutting for most or all of the different general combustion technologies. These are, in order of priority; • • • • • High-temperature furnace efficiency improvements through flame radiation enhancement and o}..),gen enrichment Heat release profiling to optimize energy transfer from the energy source to the load Refractory improvements Acid gas (primarily NOJ control, especially for conventional multiple burner arrays and catalytically assisted combustion Flame safety and stability. Furnace efficiency is important for the process he~ters that dominate refinery combustion proc~ss~s, ~s well as other combustion equipment. Efficiency and perfonnance llnproven~ents for,Process heaters can result. ill SIgnificant energy and operating cost savings and higher safety. Control of radiant sectIOn temperatures are very Important for 6 |