Mar-2004

LoTOx technology demonstration at Marathon Ashland Petroleum LLC’s Refinery In Texas City

Marathon Ashland Petroleum LLC’s (MAP) Texas City, Texas, Refinery conducted a review of several options to reduce nitrogen oxides (NOx) from its Fluid Catalytic Converter Unit (FCCU).

Jeffrey Sexton Marathon Ashland Petroleum LLC
Nicholas Confuorto, Belco Technologies Corporation
Michael Barrasso and Naresh Suchak, BOC Process Gas Solutions

Article Summary

MAP’s main drivers for reducing NOx emissions at the refinery are the Houston area NOx SIP regulations and execution of a voluntary consent decree with the USEPA. The technology search identified BOC’s LoTOx technology as a potential NOx control technology for FCC application. Although the LoTOx technology had commercially demonstrated NOx reduction on a variety of combustion and non-combustion sources, it had never been used on an FCC. However, since MAP had already installed a Belco EDV scrubber, the LoTOx technology was a feasible application. MAP approached BOC and Belco to conduct a demonstration of the combined technology at the Texas City FCC site. The goal of the demonstration was to confirm the performance of the LoTOx technology on FCC regenerator flue-gas using a Belco EDV scrubber. The demonstration was conducted October through November, 2002. The following conclusions were drawn from the demonstration at the Texas City refinery:
• NOx emissions can be reliably reduced to 10 parts per million volume (ppmv) or less through use of the LoTOx technology with the EDV Wet Scrubbing System
• The LoTOx technology can achieve NOx reduction without conversion of sulphur dioxide (SO2) to sulphur trioxide (SO3).
• Data to optimise the FCC application parameters for the LoTOx technology were collected and analysed.
• FCC catalyst particulate and sulphur compounds in the FCC flue-gas do not affect the LoTOx technology’s ozone consumption or NOx removal efficiency.
• With the LoTOx technology NOx removal efficiency can be instantaneously varied by adjusting the NOx outlet set point (which in turn adjusts the ozone injection rate).
• High NOx removal efficiency can be maintained during start-up and FCC upset conditions.
• Total emissions of NOx remained low as expected under varying inlet NOx and oxygen (O2) concentrations.

Introduction - FCC Operation at Texas City
Marathon Ashland Petroleum LLC (MAP) operates a 72,000 barrel per stream day (bpsd) refinery in Texas City, Texas. The refinery contains a Fluid Catalytic Cracking process unit (FCC) that is a UOP side-by-side design with an internal riser and bubbling bed regenerator built in 1963. Unit feedstock is topped crude, supplemented with incremental purchased gas oil. Combustion air is distributed through one inner ring and one outer ring distributor. The flue gas temperature is cooled by a steam generator and its pressure reduced by a slide valve and orifice chamber before being discharged to the atmosphere. FCC exhaust emissions are continuously monitored for nitrous oxides (NOx), carbon monoxide (CO) and sulphur oxides (SOx). Actual NOx emissions range from 50 to 150 parts per million volume dry (ppmvd) corrected to zero percent O2. A Belco EDV Wet Scrubbing System for abatement of sulphur oxides and particulate emissions was installed during the unit revamp at the beginning of 2003 (Figure 1). Belco and BOC are presently working on a Front End Engineering Design (FEED) package to install the LoTOx technology to the EDV wet Scrubbing System at the refinery.

NOx Control Requirements
The Texas City refinery is located in the Houston-Galveston Area, which is subject to increasingly stringent environmental regulations. The eight county Houston-Galveston area has been classified as a severe non-attainment area. The Texas Commission of Environmental Quality is currently proposing regulations to reduce NOx and volatile organic compounds (VOC) to improve air quality. These regulations would require FCC units to reduce NOx emissions below 40 ppmvd. If FCC emissions can be reduced below this value, the incremental reductions could offset other NOx requirements in the refinery, making it necessary to review NOx control options both independently for the FCC as well as in the framework of the overall site strategy.

In addition to the Houston NOx SIP regulations, MAP signed a voluntary consent decree with the US Environmental Protection Agency regarding new source review requirements. The consent decree requires all MAP FCC units to reduce NOx emission and meet more stringent limitations.

NOx Control Technology Evaluation
MAP conducted a technology evaluation process where several vendors and technologies were considered. During this review, the LoTOx technology was identified as a potential solution for MAP’s application. The synergy with the required Houston-area NOx reductions and the Belco EDV scrubber appeared to be a fit with the Texas City FCC. The LoTOx technology has been successfully demonstrated on flue gas originating from a variety of combustion and non-combustion sources. However, none had been from an FCC. Specific challenges related to SO3 and catalyst fines were a concern. MAP approached BOC and Belco to conduct a demonstration of the technology at the Texas City FCC site. The results of this demonstration, along with alternative technology concerns, are presented in this paper.

Available nox control technologies - Catalyst Additives
Catalyst additives have been demonstrated by the catalyst vendors for the reduction of NOx emissions from the FCC. Some refinery trials have resulted in large emission reductions; however, the overall industry experience has been mixed. In some cases, the additives have been effective, while others have seen no impact. The most difficult aspect in assessing the applicability of catalyst additives is the unpredictable performance. Lack of clear understanding of the factors that affect the operation leaves refiners at risk of non-compliant performance. Assessing current applicability does not address the issue of needing to understand how process changes such as differing feedstocks and regeneration conditions will affect performance over time.

Selective Catalytic Reduction
Selective Catalytic Reduction (SCR) involves injecting ammonia into high temperature flue gas flowing through a catalyst bed. The length of the catalyst bed and the total catalyst volume increase with required NOx conversion effectiveness. Catalysts are sensitive to poisoning due to a variety of contaminants such as sulphur compounds and metals. Long term SCR efficiency is also affected by surface deterioration (erosion) due to abrasive particulate. All of these factors are generally present in FCC exhaust and can adversely affect the SCR catalyst performance.
Furthermore, ammonia has been identified as a criteria pollutant and is undesirable in ambient air. Even low levels of ammonia are detectable by odour and, in the presence of acid gases, form ammonium salts that are sub-micron particulate matter. These salts may remain suspended in the atmosphere causing smog. The required addition of excess ammonia, or ammonia slip, into a sulphur-containing stream opens the possibility of the formation of ammonium bisulphite and ammonium sulfate salts, which become a resinous and corrosive coatings on the downstream equipment. The presence of sulphur in the flue gas can also lead to emissions opacity issues from the generation of SO3 on the SCR catalyst. Conversion rates of the SO2 in the stream can typically range from 1 to 5 percent with SCR.