Bitumen Burning In Oilfield Steam Generators

Abstract Emphasis on thermal enhanced oil recovery using steam has prompted a desire for information on oilfield steam generation techniques and fuels. In any steam project, the cost of generating steam is the single most expensive operating cost required to produce bitumen or heavy oil. Bitumen is a decidedly difficult fuel to burn in an oilfield boiler as compared to alternatives such as natural gas or propane. Problems due to fuel handling, fouling, corrosion, and emissions are inevitably encountered and generally lead to poor system performance. However, fuel costs and supply problems often influence fuel selection, especially in remote regions. For these reasons, bitumen burning has been considered as a viable option. An investigation on the bitumen burning experiences at four projects, supported by the Alberta Oil Sands Technology and Research Authority (AOSTRA), was performed to better understand the problems inherent in using produced bitumen as a fuel for steam generation, both generally and with respect to the generator's design and operation. Several aspects of boiler operation are covered and operational histories were considered. It was found that bitumen burning is nor difficult with the proper equipment and modifications to steam generating facilities. The major problems encountered were excessive pollutant emissions, damage due to corrosion, and increased maintenance. Introduction Steam stimulation production of the Alberta oil sands accounts for the majority of the present oil sand in-situ pilot projects. High pressure steam is injected into the reservoir in order to enhance the in-situ oil recovery. There are, at present three commercial and numerous pilot in-situ thermal recovery operations underway in Alberta. The Alberta Oil Sands Technology and Research Authority (AOSTRA) has participated in several pilot plant Projects. These pilots have steam generators located in the entire major oil sand deposits of the province. Most steam generators at AOSTRA-sponsored pilots are of the conventional once-through horizontal design. Steam generators of the once through type are used almost exclusively for thermal oil recovery. They were developed for such use and differ from a true utility boiler in that they have no steam separating, thus recirculation and blowdown are not required. Once-through generators are somewhat simpler in construction and operation than utility boilers making them more desirable for remote oil fields. Fuel can consist of natural or produced gas, fuel oil, propane, bunker crude, or bitumen. There are four AOSTRA supported pilots which have used produced bitumen as a steam generation fuel. Problems due to fuel handling, fouling, corrosion, and emissions are inevitably encountered when burning bitumen and generally lead to poor system performance. However, fuel costs and supply problems often influence selection, especially at remote locations. Bitumen Combustion All fuels, whether in solid, liquid, or gaseous state are composed of combustible and non-combustible elements. The combustible elements are; hydrogen, carbon, and sulphur. The non-combustible elements are; moisture, ash, carbon dioxide, and other trace elements. Fuel oils, which include bitumen, are derived from petroleum and their main components are carbon and hydrogen combined with hydrocarbons, small amounts of oxygen, sulphur, nitrogen, and some traces of ash.