BY: TIMOTHY R. FELTHOUSE, Ph.D; MARIO P. DIGIOVANNI, P.E.; JOHN R. HORNE

AND SARAH A. RICHARDSON

PRESENTED AT: THE AIChE CLEARWATER CONVENTION 2011

PHOSPHATE FERTILIZER & SULFURIC ACID TECHNOLOGY CONFERENCE CLEARWATER BEACH, FLORIDA JUNE 10-11, 2011 

# IMPROVING SULFURIC ACID
PLANT PERFORMANCE

THROUGH NEW SHAPE & HIGHER ACTIVITY
CATALYSTS2 TABLE OF CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

CATALYST PROTOTYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

GEAR TM CATALYST FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

LOWER SO 2 EMISSIONS AND INCREASED ACID PRO DUCTION . . . . . . . . . . . 10

ENERGY SAVINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

MECS CATALYST PRODUCT PORTFOLIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 LIST OF FIGURES

Figure Page

1. MECS Sulfuric Acid Catalyst Shap es Range from (left to right) New

13-mm GEAR TM Ribbed Ring, 12-mm XLP Ri bbed Ring, 10-mm Ring,

and 6-mm Pellet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Predicted Pressure Drop Build-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. SO 2 Concentration Gradients for GEAR TM Catalyst Cross-Section at 475 o C

and 11.0% SO 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4. GEAR TM Catalyst Requires Less Catalyst than XLP Catalyst for the Same

Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5. GEAR TM Catalyst Reduces SO 2 Emissions Compared to Same Volume of XLP Catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6. Random Catalyst Packing for GR-330 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7. Relative Pressure Drop for LP-110, LP-120, XLP, and GR-330 Catalysts . . . . 13

LIST OF TABLES

Table Page

1. Operating Conditions for the Catalyst GR-330 Prot otype . . . . . . . . . . . . . . . . . 6

2. Pass 1 Catalyst Sleeve Operating Conditions within a Converter . . . . . . . . . . . 8

3. GEAR TM Catalyst Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4. Emissions Comparison for XLP and GEAR TM Catalysts . . . . . . . . . . . . . . . . . . 12

5. Estimated Savings for a Full Converter of GEAR TM Catalyst in a 3300

STPD 3X1 IPA Acid Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6. MECS New Catalyst Product Portfolio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 ABSTRACT

A new line of sulfuric acid catalysts called GEAR TM has been developed by MECS, Inc. that offers improved performance to the sulfuric acid industry. These catalysts combine a new low-pressure drop ribbed-ring shape with higher activity for a combination of increased energy savings and lower overall plant SO 2 emissions. Pass 1 plant tests with a prototype of our new shap e ran for 27 months during which the pressure drop rose from 4 to 12 in W. C., less than half of the typical pressure drop rise. PeGASyS tests of the plant confirmed conversi on performance of the ca talyst in pass 1. This paper presents several cases to demonstr ate the advantages of these new catalysts.5 INTRODUCTION

On December 31 st of 2010, MECS, Inc. became a wholly owned subsidiary of DuPont and part of the company’s Sustai nable Solutions busines s. The combined resources of MECS and DuPont create an expanded portfolio to enhance the safety, reliability, and environmental sustaina bility of custom ers’ facilities.

MECS has been in the sulf uric acid catalyst business since the 1920’s. Over the past 90 years, catalyst has evolved from pelle ts to energy-saving rings to low-emission cesium-promoted catalyst. As energy saving s and environmental concerns create new operational and design challenges for sulfuric acid plants, innova tions in catalyst technology can provide the resolution. Over the past few years, MECS has designed, developed, and tested in labor atory and acid plant operations several new catalyst shapes

and formulations. Results from these catalyst evaluations led to significant improvements in shape, dust cap acity, pressure drop, and activ ity. As a result of these catalyst performance improvements, MECS intr oduces in this paper their next generation of sulfuric acid catalysts known as GEAR TM catalysts.

This paper presents the findings of aci d plant and laboratory evaluations leading

to the new line of GEAR TM catalysts. Based on comparisons with MECS XLP-220 and XLP-110 catalysts, advantages of these GEAR TM catalysts will be demonstrated. Figure 1 depicts some of the shapes in the new ME CS sulfuric acid catalys t portfolio including

the new GEAR TM catalyst (13-mm GR-330).

Figure 1. MECS Sulfuric Acid Catalyst Shapes Range from (left to right) New

13-mm GEAR TM Ribbed Ring, 12-mm XLP Ribbed Ring, 10-mm Ring, and

6-mm Pellet.6 RESULTS

Catalyst Prototypes

As is often the case in scientific discovery, it takes a few trials to reach the desired results. The development of the GEAR TM catalyst products took se veral years and a few different prototypes to produce a catalyst fa mily with the desired characteristics.

A plant trial provided valuable inform ation regarding pressure drop and dust handling capability of improved MECS catalys t. A bed of 13-mm catalyst prototype was placed in the first pass of a small sulfur-burni ng sulfuric acid plant and run for 27 months at the operating conditions shown in Table 1.

Table 1. Operating Conditions for the Catalyst GR-330 Prototype.

Converter Diameter, ft. 9.5
Production Rate, STPD 130 Pass 1 GR-330 Prototype Volume, L 4200
Gas Strength, %-SO 2 8.9 to 9.5

Inlet Temperature, o C ( o F) 411 (772)

PeGASyS testing that was done when the catalys t was first charged and at the conclusion of the pass 1 trial confirmed the catalyst performance. Clean bed pressure drop was

measured at 4 in W. C. After 27 months of operation, the pressure drop in pass 1 was 12 in W. C. The pressure drop build-up was fit to MECS’ proprietary ash pressure drop build-up model showing a result comparable to 15-ppm ash content in th e sulfur feed. In contrast, the pressure drop of XLP- 220 catalyst in pass 1 of this plant started out at

7 in W. C. and reached 25 in W. C. in 18 months. Figure 2 shows these pressure drop build-up curves as a percent of clean bed pre ssure drop. The dust model results show that the larger shape, the GR-330 prototype, exte nds the operating time by at least 8 months, which is 40% longer run time.7 0% 100% 200% 300% 400% 500% 600% 700% 800% 900% 1000%

0 3 6 9 12 15 18 21 24 27

Operating Time, Months%-Relative Pressure Drop XLP-220

GR-330 Prototype

Figure 2. Predicted Pressure Drop Build-up.

A more active “GR” formulation is another feature developed for the GEAR TM
catalysts. To evaluate this formulation with respect to catalyst “stickiness” and activity sustainability, a two year plant trial was empl oyed. Four 36-inch deep cylindrical sleeves were filled with XLP-shaped (12-mm ribbed ri ng) catalyst containing this new, more active formulation. The sleeves were placed in the four quadrants of pass 1 of a large sulfur-burning sulfuric acid plant and opera ted under the conditions shown in Table 2. Two additional sleeves of standard production XLP-220 catalyst were also placed in pass 1.8 Table 2. Pass 1 Catalyst Sleeve Operating Conditions within a Converter.

Converter Diameter, ft. 42 Typical Plant Prod uction Rate, STPD 3600
Gas Strength, %-SO 2 11.5

Inlet Temperature, o C ( o F) 428 (802)

Sleeve Diameter, ft. 0.67 Sleeve Length, ft. 3.0

Pass 1 GR-Formulation-Protot ype Sleeve Volumes, L 30
Sleeve Distances From Bed Center, ft. 21 Sleeve Operating Time, months 24

After 24 months of operation, the sleeves were recovered, inspected for relative “stickiness” with respect to the entrained dus t, and sieved to separate the dust from the catalyst. Four zones consisti ng of different bed depths of catalyst were evaluated from

each sleeve to determine where the dust accumulated. As expected, the “GR” formulation catalyst and the XLP-220 catalyst had comparable amounts of dust at the different sleeve depths. The more active “G R” formulation catalyst, along with the XLP220 catalyst, was free from any “crusting” from the dust.

Catalyst activity of the “GR” formulation catalyst sleeve samples was determined for each of the zones. As expected, the high dust zones at the top of the sleeves showed the greatest reduction in activity after tw o years of operation as measured by the

differential conversion of SO 2 . In the lower three zones of the four sleeves the “GR” formulation catalyst showed a higher activity level relative to traditional MECS catalysts following two years of operation and was superi or to XLP-220 catalyst in maintaining its overall activity level.

GEAR TM Catalyst Features

The GEAR TM catalyst shape evolved from both computational and comparative small pilot plant scale results on five diffe rent ribbed ring catalysts shapes. The computational results provided relative catal yst effectiveness as a function of each of these ribbed catalyst shapes. Figure 3 depicts SO 2 concentration gradients (Comsol Multiphysics Finite Element Modeling) for the GEAR TM shape indicating good gas penetration into the core of the catal yst from the outer and inner surfaces.9 Figure 3. SO 2 Concentration Gradients for GEAR TM Catalyst

Cross-Section at 475 o C and 11.0% SO 2 .

Pilot plant scale (20 to 30 L) catalyst volumes afforded comparative pressure drops and

kinetic reaction rates for each of these five catalyst shapes. From these comparative tests,

the GEAR TM shape was chosen because it showed the best set of attributes. Table 3 highlights the features of MECS’ new GEAR TM catalyst. Note that the GEAR TM catalyst comes in two sizes, providing the best balance of pressure drop and activity for various plant operating conditions.

Table 3. GEAR TM Catalyst Features.

Catalyst GR-330 GR-310
Nominal Diameter, mm 13 11

Formulation Advanced Advanced

Ignition Temperature Range, o C ( o F) 350-360 (662-680) 350-360 (662-680)
%-Lower Pressure Drop than XLP 30 15

The GEAR TM family of catalyst products can improve sulfuric acid plant performance by lowering SO 2 emissions, increasing acid pr oduction, extending operating10 time, and saving energy. GEAR TM is an acronym for the following catalyst features:

G = G eometrically Optimized

E = E nhanced Surface Area

A = A ctivity Improvement

R = R educed Pressure Drop

Advantages of the GEAR TM catalysts are demonstrated in the next two sections. Several examples compare the performance of GEAR TM catalyst to XLP catalyst.

Lower SO 2 Emissions and Increased Acid Production

The combination of enhanced surface area and activity improvement conferred by the advanced formulation and shape reduces the required catalyst volume. The bar graph in Figure 4 compares the relative volum es of XLP-220/XLP-110 catalyst and GR330/GR-310 catalyst for the same conversion. If gas strength remains constant and

GEAR TM catalyst volume is adjusted to meet th e same emissions as XLP catalyst, then

the GEAR TM catalyst will require 5 to 15% lower catalyst volume. The trend in Figure 4

shows that GEAR TM is more effective at higher ga s strengths than XLP catalyst.

80% 90% 100% 110% 120% 130% 140%

10.0 10.5 11.0 11.5

Percent SO 2Relative Percent Catalyst Loading. GEAR(TM) Catalyst

XLP Catalyst

Figure 4. GEAR TM Catalyst Requires Less Catalyst than XLP Catalyst for the Same Conversion.11 If the volume of GEAR TM catalyst is kept the same as XLP catalyst, then the increased catalyst activity of GEAR TM catalyst results in 10 to 30% lower emissions for a given gas strength, depending upon the target em issions level. These relationships are shown in Figure 5. Alternatively, for a given catalyst volume, using GEAR TM catalyst and increasing the gas strength can facilitate 5 to 6% higher plant capacity with the same

SO 2 emissions. For the lowest overall emissi ons, use of SCX-2000 in the final pass or passes is recommended.

0 50 100 150 200 250 300

9.5 10.0 10.5 11.0 11.5 12.0

Inlet %-SO 2 Gas StrengthSO2Emissions, ppmv XLP Catalyst

GR Catalyst

Figure 5. GEAR TM Catalyst Reduces SO 2 Emissions Compared to Same Volume of XLP Catalyst

.

To illustrate further the SO 2 emissions reduction afforded by the GEAR TM
catalyst, four catalyst design cases were c onsidered for a new 3X1 IPA sulfur burning plant. Table 4 summarizes the four cases that vary by catalyst type and pass 4 inlet temperature. Catalyst loading remained consta nt for all of the cases in this comparison. Compared to XLP catalyst, use of GEAR TM catalyst offered 20% lower SO 2 emissions. The plant SO 2 emissions for the design with GEAR TM catalyst and SCX-2000 were 65% lower than the XLP catalyst design. For u ltra-low emissions of 65 ppm, SCX-2000 was used in both the third and fourth passes with GEAR TM catalyst in the upper passes.12 Table 4. Emissions Comparison for XLP and GEAR TM Catalysts.

Case 1 Case 2 Case 3 Case 4

Pass 1 XLP-220 GR-330 GR-330 GR-330

Pass 2 XLP-110 GR-310 GR-310 GR-310

Pass 3 XLP-110 GR-310 GR-310 SCX-2000

Pass 4 XLP-110 GR-310 SCX-2000 SCX-2000

Pass 4 Inlet Temperature, o C ( o F) 425 (795) 420 (790) 390 (735) 390 (735)

Overall Conversion, % 99.812 99.849 99.935 99.953

SO 2 in Stack, ppmv 260 210 90 65

%-Reduction 0% 20% 65% 75% Basis: 11.5% SO 2 3X1 IPA Sulfur Burning Plant

Energy Savings

From the GR-330 prototype dust build-up results above (Figure 2), the pressure drop difference between GR-330 and XLP-220 is likely to widen as dust accumulates on the catalysts over time. These results in dicate GR-330 should provi de a greater energy savings over time in both pressure drop and extended operating time. Placing either GR330 or GR-310 catalysts in the lower passes will increase further the annual savings from the pressure drop advantage of these catalysts. The GEAR TM catalyst geometry improves catalyst spacing in the converter. Evid ence for this improved spacing comes from comparative pressure drop curves for the GEAR TM catalysts compared to other MECS catalyst shapes. The random packing of the GEAR TM catalyst is shown in Figure 6.

Figure 6. Random Catalyst Packing for GR-330.13 The optimization of the GEAR TM catalyst shape resulted in a lower pressure drop catalyst. One at a time, each of the catalysts in MECS’ portfolio were packed into a 6- inch vessel and the pressure drop was measur ed as a function of volumetric flow rate over the entire range of gas flow spa nned by the Ergun equation (Ergun, 1952). With temperature and pressure recorded over th e entire flow range (0 to 1000 SLPM), the Ergun k 1 and k 2 coefficients were fit by regression of the pressure drop values. Figure 7 displays the relative pressure drop against the %-design gas flow rate for LP-110, LP120, XLP, and GR-330 catalysts.

0% 50% 100% 150% 200% 250%

50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150%

Percent of Design Gas Flow RatePercent of XLP Design Pressure Drop LP-110

XLP-110

LP-120

GR-330

Figure 7. Relative Pressure Drop for LP-110, LP-120, XLP, and GR-330 Catalysts.

The pressure drop advantage of GEAR TM catalyst can be more clearly shown by calculating the energy savings. A 3300 STPD sulfur burning 3X1 IPA acid plant with

11.5% SO 2 gas strength to pass 1 was used for this example. Table 5 shows the pressure drop savings achieved using GEAR TM catalyst compared to XLP. With Florida electricity costs estimated for industrial use at $0.10/kWh (U. S. Energy Information Administration, 2010), the resulting savings from utilizing GEAR TM catalyst equates to $20,000 per inch of pressure drop saved.14 Table 5. Estimated Savings for a Full Converter of GEAR TM Catalyst

in a 3300 STPD 3X1 IPA Acid Plant.

Production Rate, STPD 3300
Pass 1 Gas Strength, %-SO 2 11.5
Gas Velocity to Pass 1, SLFM 100 GR-330/GR-310 Catalyst Pre ssure Drop Savings vs. XLP 15% GR-330 Catalyst Pressure Drop Savings vs. XLP 30% Estimated Electricity Cost, $/kWh $ 0.10 Estimated Annual Savings, $/In W. C. 20,000 $

MECS Catalyst Product Portfolio

As shown in Table 3, two new GEAR TM shapes have been added to the MECS catalyst product portfolio. Ca talyst screening trial test s of the GR-330 and GR-310 catalysts showed these products to have the same durability and low screening losses as

XLP-220 and XLP-110.

Additionally, the LP-110 formulation has been enhanced to create a new LP-310 catalyst product with the same ring size and shape as LP-110 but in a more active formulation. The LP-310 catalyst can reduce SO 2 emissions or increase acid production compared to LP-120, LP-220, and LP-110 in lower velocity converters.

MECS’ new product portfolio is show n in Table 6. The new products are highlighted in red.

Table 6. MECS New Catalyst Product Portfolio.

Ribbed Rings Smooth Rings Pellets Cesium

GR-330 LP-310 T-11 SCX-2000

GR-310 LP-220 XCs-120

XLP-220 LP-120 Cs-110

XLP-110 LP-11015 CONCLUSIONS

The GR-330, GR-310 and LP-310 catalysts wi ll be available from MECS starting in the third quarter of 2011. As the data in this paper have shown, GEAR TM catalysts provide a range of benefits for impr oved acid plant performance: lower SO 2 emissions, increased acid production, exte nded operating time, and ener gy savings. Plants with lower velocity converters similarly can bene fit from increased acid production or lower emissions through use of the LP-310 product.

Improved GEAR TM catalysts are the latest editio n to MECS’ portfolio of products for the sulfuric acid industry. MECS has t echnologies in this industry that include sulfuric acid plant processes, heat recovery systems for sulf uric acid plant processes, wet gas scrubbing, mist elimination, air preheating, corrosion resistant metals for sulfuric acid service, engineering and c onsulting services, and PeGASyS plant analysis. In 2011 MECS now combines these products and services with the worl d-class sulfuric acid plant knowledge, experience, and process safety mana gement of DuPont. MECS is ready to meet customer and technology challe nges in the twenty-first century.16 REFERENCES

Ergun, S, 1952. Fluid Flow through Packed Co lumns. Chem. Eng. Progr. 48(2): 89-94.

U. S. Energy Information Administration, 2010. Average Retail Price of Electricity to Ultimate Customers by End-Use Sect or, by State, published online at: http://www.eia.doe.gov/cneaf/ele ctricity/epm/epmxlfile5_6_a.xls , January 2011 data

released 2011 March 11.

©MECS, Inc. 2011. Information herein is confidential and may not be used by, reproduced for, or revealed to third parties, except in acco rdance with contract or other wr itten permission by MECS, Inc.

The DuPont oval logo and the miracles of science(TM) are trademarks or registered trademarks of DuPont

or its affiliates.