Annual Meeting March 21-23, 2010 Sheraton and Wyndham Phoenix, AZ

AM-10-106 An Overview of the FCCU SCR Experience at CITGO’s Lemont Refinery

Presented By: Brian Slemp Processes Technologist CITGO Petroleum Corporation Lemont, IL Matt Cordina Area 1 – Operations Process Engineering Group Leader CITGO Petroleum Corporation Lemont, IL Dennis Salbilla Sales Manager of Industrial Processes Haldor Topsøe A/S Houston, TX

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An Overview of the FCCU SCR Experience at CITGO’s Lemont Refinery Co – Authors: Mr. Brian Slemp Processes Technologist CITGO Petroleum Corporation Lemont, IL Mr. Matt Cordina Area 1 - Operations Process Engineering Group Lead CITGO Petroleum Corporation Lemont, IL Mr. Dennis L. Salbilla Sales Manager of Industrial Processes Haldor Topsoe, Inc. Houston, TX Abstract: A SCR (Selective Catalytic Reduction) unit was installed on the CITGO Lemont FCCU in 2007 with flue gas entering the unit for the first time in early December 2007. The existing ESPs (Electrostatic Precipitators) were taken out of service resulting in a “high dust” content flue gas SCR design. This required a custom SCR catalyst that would withstand the erosive environment and still perform well over a 5 – year continuous run. The FCCU SCR unit has been in service for over two years without any maintenance outages. NOx reduction is excellent with outlet NOx values below 20 ppmvdc @ 0% O2. Pressure drops across each of the two separate SCR catalyst layers are less than 1” WC.

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BACKGROUND Refiners are obligated to comply with requirements of the Clean Air Act, originally passed into law in 1970, regarding harmful emissions. The law requires industry to install pollution control technology limiting pollutants such as NOx, SOx, CO, VOC, lead and particulates1. NOx, in particular, is linked to the formation of ground – level ozone (smog) to which is attributed respiratory problems in healthy people and exacerbation of breathing problems like asthma in children and the elderly. In 1997, the Clean Air Act was amended and became more stringent citing a 0.08 ppm {8 – hour average} ozone standard from a 0.12 ppm {1 – hour average} ozone standard. As refineries continued to debottleneck and increase throughputs with the addition of new process units, they became subjected to New Source Review (NSR). This scenario required refiners to implement Best Available Control Technologies (BACT) which includes Selective Catalytic Reduction (SCR)2. To date, there are 24 U.S. refining companies that elected to enter into consent decrees with the Environmental Protection Agency accounting for approximately 88% of the domestic oil refining capacity or roughly 14.8 million barrels per day. These settlements involve 99 refineries spread across 29 states with annual emission reductions estimated at 87,000 tons of NOx and 250,000 tons of SOx

3. In January 2005, CITGO Petroleum entered into a Consent Decree with the U.S. Environmental Protection Agency. The refiner agreed to reduce NOx emissions from the Lemont Refinery’s Fluid Catalytic Cracking Unit (FCCU) to 20 ppmvdc on a 365-day rolling average and 40 ppmvdc on a 7-day rolling average, both at 0% reference oxygen (O2). Reductions in SOx emissions were also agreed at 25 ppmvdc on a 365-day rolling average and 50 ppmvdc on a 7-day rolling average, again based at 0% O24. In order to achieve these emission targets, CITGO installed, on the flue gas line, a SCR Unit for NOx reduction immediately upstream of a Wet Gas Scrubber, which removes particulates, SOx and ammonia. An existing ESP was removed from service after startup of the new Wet Gas Scrubber. The ESP was no longer required because of the High Dust SCR unit offered by Haldor Topsoe and the state of the art Wet Gas Scrubber offered by GEA Bischoff. KTI Corporation from Houston, TX was selected as the Engineering, Procurement and Construction firm. DESIGN The design of a FCCU SCR comes with some unique challenges. These include:

• Two-phase flow as catalyst fines are entrained in the flue gas • Continuous operation targeting a 4 to 5 year run life • Low pressure drop in a dusty operating environment

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Once the design parameters are provided by the refiner, sizing of the SCR catalyst is determined. These data include the following information in Table 1:

Flue Gas Flow Rate, pounds per hour 1,198,137 Temperature, degrees F 615 Pressure, inches of WC 30 NOx, ppmvdc @ 0% reference O2 315 SOx, ppmvdc @ 0% reference O2 1555 H2O, vol. % 7.85 O2, vol. % 2.77 CO2, vol. % 13.64 N2, vol. % 76.84 Ar, vol. % 0.90 Particulate, pounds per hour 1,000 Flue Gas Flow Maldistribution, + % RMS 15 NH3 to NOx Maldistribution, + % RMS 5 Temperature Maldistribution, degrees F 25

Table 1 Selective Catalytic Reduction (SCR) is an end-of-pipe technology used for NOx destruction characterized by high single-pass removal efficiency5. Figure 1 shows the typical Process Flow Diagram of a SCR system. Ammonia is injected into the flue gas at slightly above the molar equivalent ratio as its NOx concentration to react on the catalyst producing nitrogen and water. Ammonia flow is automatically controlled by feedback control measuring outlet NOx downstream of the SCR catalyst.

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Figure 1

The main first order reactions are as follows: 4 NO + 4 NH3 + O2 4 N2 + 6 H2O ΔHo = -1,627.7 kJ/mol NO + NO2 + 2 NH3 2 N2 + 3 H2O ΔHo = -757.9 kJ/ mol 6NO2 + 8NH3 7N2 + 12 H2O ΔHo = -3067.1 kJ/ mol NO (nitrogen monoxide) is the primary NOx component in the flue gas, meaning that the first equation above this the more significant one6. Reaction rates are indicative of the Arrhenius equation that describes temperature dependent reactions. The temperature range for SCR can vary between 375°F and 1,000°F for NOx reduction; however, it is necessary to operate at temperatures above 600°F-620°F to avoid forming Ammonium Bisulfate (ABS) when SO3 is present in the flue gas7. Figure 2 contains CITGO Lemont’s FCCU SCR Ammonia Bisulfate formation curve as a function of Inlet SO3.

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CITGO LEMONT FCCU ABS Temperature °F vs Inlet SO3

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Haldor Topsoe’s design philosophy for FCCU SCR applications calls for a vertical down flow unit. This takes advantage of gravity to address the catalyst fines entrained in the flue gas. Turning vanes are required to prevent uneven stratification of the solids and maintain a uniform velocity profile leading up to the inlet face of the SCR catalyst.

Figure 3

The CITGO Lemont FCCU SCR unit has these characteristics and is shown in Figure 3. Two catalyst layers each containing 40 modules with 1 meter deep of DNX-858 catalyst

are employed. The size of one module is approximately 2 meters wide by 1 meter high by 1 meter deep in the flow direction. A set of static mixers along with the NH3 injection lances are located at the CO Boiler outlet, well upstream of the SCR Catalyst, to provide adequate mixing time for the ammonia to blend completely with the flue gas prior to reaction on the catalyst surface. The cross-sectional area of the catalyst bed combined with the catalyst pitch and flue gflow rate determine the pressure drop. HighNOx reduction and a low pressure drop

as

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Figure 3

requirement results in a large catalyst volume. The ideal SCR catalyst is one which performs reliably in the FCCU’s erosive environment. This catalyst should have a thick robust wall, wide pitch for low pressure drop 8 and maximum reactive surface area . An example of this catalyst is shown below in Figure 4 followed by its typical properties.

Figure 4

DNX – 958 5 – 10 wt. % V2O5 2 – 4 wt. % WO3 5.5 mm Hydraulic Diameter 1.0 mm Wall Thickness, t 7.2 mm Cell Pitch, Pc 7.0 mm Plate Pitch, Pp 14.4 mm, Wave Length, L

The Haldor Topsoe DNX-858 catalyst utilizes a tri-modal pore size distribution containing Macro pores, Meso pores and Micro pores for activity retention in this dust laden environment. FCCU catalyst entrained in the flue gas is typically fines having an average particle size below 10 microns as well as full range catalyst, with an average particle size of 70 microns during an upset. The fines are able to fill the Macro pores similar to how marbles fill a vase. At some point, the Macro pores accept the maximum amount of catalyst dust yet NOx and NH3 in the flue gas can still diffuse into these pores through the remaining void space and complete the reduction reaction on the active sites of the catalyst surface.

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A picture of the catalyst’s surface taken with the aid of a high magnification microscope is presented in Figure 5. The tri-modal pore sizes are identified relative to each other.

A: Macro pores

200 μm

5 µm

B: Intermediate pores

200 nm

C: Micro pores

The three pore size regimes visualized by scanning electron microscopy (SEM).

A: Macro pores B: Meso (Intermediate) pores C: Micro pores

Figure 5

After deciding on a catalyst and determining the required volume configured in two identical layers, computational fluid dynamics is used to further develop the design as shown in Figure 69. Root Mean Square maldistributions for flue gas flow, NH3:NOx and temperature are quantified and corrected within acceptable tolerances, ±15%, ±10% RMS and ±20 degrees F, respectively. Turning vanes, static mixers and adequate mixing time enable the even distribution of flow and NH3 prior to entering the first layer of SCR catalyst.

Figure 6 CFD modeling leads to scale modeling for cold flow verification of the design. Location and orientation of the turning vanes are discovered through repeated smoke and dust tests. Figure 7 shows the Plexiglas scale model of the CITGO Lemont FCCU SCR with all the components in their optimal location. These pictures provide close-up details of the turning vanes immediately upstream of the SCR catalyst.

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Figure 7

With the design validated through CFD and scale model testing, the SCR components are built for field erection. An example of this scale-up work focuses on the duct containing the Haldor Topsoe patented STARMIXER® static mixers and NH3 injection lances. The following photos in Figure 8 show a side-by-side comparison of the scale model and the actual equipment prior to installation.

Figure 8

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The SCR reactor contains two identical catalyst layers. Each layer has 40 Haldor Topsoe VE422AA modules, as described in Figure 9, loaded with DNX-858 catalyst arranged 5 long by 8 wide. The dimensions of the individual modules are shown below and translate to a SCR Reactor Cross Sectional Area of 31 feet long by 25 feet wide.

The weight of each module approaches 2,000 pounds and therefore is a challenge to move and set in place. Once the crane lifts the module to the loading door elevation, a pallet mover is used to pick and set the module inside the reactor. The weight of each module is supported by structural steel beams. Grating is used to construct a floor inside the SCR reactor. The seal is made at the base of the module frame using 2-inch-wide sealing gutters constructed from sheet metal. Figure 9

Figure 10 Figure 11

Figures 10 and 11 were taken during the SCR catalyst loading. The weight of the catalyst modules is distributed across a pedestal frame which rests on structural steel supports. The distance between the retractable soot blower rakes and the top of the catalyst modules is only a few feet. The seal is placed at the outer perimeter of the catalyst bed, sandwiched between module frame and the wall. This creates a small space between the wall and the modules so that installation of the catalyst dust deflectors can be completed with relative ease. The dust screens prevent catalyst fines from collecting in the annular space between the walls and the modules by directing all material of the flue gas to pass through the catalyst bed. Screens with wire mesh are incorporated into the design to provide additional protection during future inspections and maintenance outages. Figures 12 and 13 offer close – up images of the dust deflectors and protective wire mesh screens.

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Figure 12 Figure 13

Dust removal from the SCR catalyst and re-entrainment back into the flue gas is achieved with the use of steam soot blowers. The large cross-sectional area of the SCR catalyst requires a soot blower system with retractable rakes, like the ones shown in Figures 14 and 15, to keep catalyst build – up to a minimum. The soot blowers cycle once every 8 to 12 hours depending in the amount of particulates in the flue gas. During upset conditions, the soot blowers can sweep the catalyst bed more frequently until normal operations are re-established.

Figure 14 Figure 15

Operational Performance Flue gas was initially routed to the Wet Gas Scrubber through a bypass line that circumvented the CO Boiler and SCR Reactor prior to commissioning the SCR. In early December 2007, when the FCCU SCR Reactor was put into service, the flue gas was cut over hot to the CO Boiler and SCR. Ammonia injection started when the catalyst reached operating temperature. There were no operational issues with the startup or with the two subsequent years of operation.

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The SCR Reactor has performed well on every design parameter. The key design parameters are shown below: 1. NOx Limit: Consent Decree requirements of 40 ppmv 7-Day rolling average max

and 20 ppmvdc 365-day rolling average max (both corrected to 0% O2). Both Consent Decree NOx requirements have been met since unit startup. The 365-day rolling average NOx limit has been met and currently is 12 ppm. The 7-day rolling average NOx limit has also been met; however, startup and shutdown procedures were modified because the 600 °F minimum temperature, required for ammonia injection, cannot be maintained with only the CO Boiler in operation.

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Figure 16

The following graphs illustrate the excellent NOx reduction achieved by the CITGO Lemont FCCU SCR.

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NOx Conversion Efficiency

80%

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Figure 17 2. Pressure Drop: The SCR has a total system design maximum pressure drop of 5

inches of H2O and catalyst bed pressure drop of 1.5 inches H2O per layer. The total system pressure drop, which includes the ammonia injection grid, flow rectifiers, turning vanes, soot blowers and catalyst beds, is measured at 2 – 2.5 inches of H2O. This is well below the design value of 5 inches of H2O. The pressure drop across each catalyst bed is measured at 0.8 inches of H2O, which is also significantly below the design value of 1.5 inches of H2O.

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SCR dP

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Figure 18

3. SO2 to SO3 Oxidation Rate: Design Maximum 0.6% SO2 conversion to SO3. In January of 2009, about 1 year after startup, a performance test was conducted on the SCR Reactor. It showed that the SO2 conversion to SO3 was 0.55%, which was slightly lower than the design maximum.

4. Unit turndown: Minimum SCR operating temperature of 600 °F and minimum

flue gas flow of 50% design.

The unit has operated at a wide variety of rates with no adverse effect on NOx reduction or ammonia slip. Additionally, the unit has operated at low rates for extended periods of time (weeks) with no detrimental effects on pressure drop even when rate is restored to maximum. Therefore, at reduced rates the turndown flow is well distributed preventing catalyst buildup and plugging. The SCR has not been run for extended periods of time at low temperatures. The minimum design temperature is 600 °F; however, the SCR Reactor inlet temperature is rarely less than 630 °F.

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SCR Inlet Temp

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Figure 19

5. Run Length:

The catalyst is designed for a five year run length. Currently, the CITGO Lemont FCCU SCR unit has operated for 2 years with no operational issues.

Conclusion Operational data show that with the use of a properly designed SCR Reactor and catalyst, that very low levels of NOx emissions are possible in FCCU’s that have high NOx, SOx and particulates in the flue gas. At the CITGO Lemont FCC, the SCR Reactor has operated two years with trouble free operation and low pressure drop even though the catalyst operated in a high particulate atmosphere because there is no ESP upstream of the SCR. Data are still being gathered to show that 5-year run lengths are achievable for this type of service; however, they should be possible with Haldor Topsoe’s experience in applications with high SOx, NOx and particulates.

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Bibliography

1. www.epa.gov/air/caa/ Web Site. Clean Air Act of 1970, public law 91 – 604.2. www.epa.gov/air/caa/ Web Site. Clean Air Act of 1990, public law – 101 – 549.3. www.epa.gov Web Site. Petroleum Refinery National Priority Case Results.4. “U.S. Announces Clean Air Agreement with CITGO Petroleum Corp.”, Press

Release, United Stated Environmental Protection Agency, October 6th, 2004.5. Ahmad, S., Lindenhoff, P., and Slaughter, J.D, “Experience with Design,

Installation and Operation of a SCR Unit after a FCCU”, National Petrochemicaland Refiners Association, March 13 – 15, 2005, San Francisco, California.Technical Paper AM – 05 – 03.

6. Walker, J. S., and Salbilla, D. L., “Analysis of NOx Reduction Techniques on anEthylene Cracking Furnace”, National Petrochemical and Refiners Association,March 14 – 16, 2004, San Antonio, Texas. Technical Paper AM – 04 – 41.

7. Lack, R. and Salbilla, D.L., “Technology, Allowances and Credits: Componentsof a Sound NOx Reduction Strategy”, Shaw/ Stone and Webster, Inc. FourteenthAnnual Refining Seminar, October 2002, Philadelphia, Pennsylvania. Pages 1 –6.

8. Damgaard, L., Widroth, B. and Schröter, M., “Control Refinery NOx withSCRs”, Hydrocarbon Processing, November 2004. Pages 39 – 42.

9. Jørgensen, J., “CITGO FCCU SCR Gas – Flow Model Study: Final Report”,FORCE Technology, Brøndby, Denmark. November 11, 2005. Pages 27 – 33.