How to Effectively Manage and Reduce Emissions in Sulfuric Acid ...

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ScienceDirect Procedia Engineering 138 (2016) 199 – 205

“SYMPHOS 2015”, 3rd International Symposium on Innovation and Technology in the Phosphate

Industry

How to effectively manage and reduce emissions in sulfuric acid plants using state-of-the-art MECS® Catalysts Sarah Richardson, Andrea Trapet, Tom Brouwers* MECS, Inc., St. Louis, Missouri MECS BVBA, Brussels, Belgium

Abstract Major sulfuric acid plant producers worldwide have installed MECS® Catalyst since the 1920s. Over the past 90 years, the dedicated Research and Development team at MECS, Inc. (MECS) has evolved catalyst from pellets to energy-saving rings to low-emission cesium-promoted catalyst. As energy savings and environmental concerns create new operational and design challenges for sulfuric acid plants, innovations in catalyst technology provide the solution. This paper will detail the MECS® Catalyst portfolio of vanadium-based and cesium-promoted catalysts for sulfuric acid, including the latest innovations, GEAR® catalyst and improved formulation cesium catalyst. The benefits of lower SO2 emissions, increased acid production, energy savings, and longer production cycles through utilization of these contemporary catalyst products will be explored. The effective performance of MECS® Catalysts will be highlighted through several case studies that demonstrate low SO 2 emissions. © by Elsevier Ltd. by This is an open © 2016 2015Published The Authors. Published Elsevier Ltd.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of SYMPHOS 2015. Peer-review under responsibility of the Scientific Committee of SYMPHOS 2015 Keywords: Type your keywords here, separated by semicolons ;

1. A Rich History of Catalyst Developments Driving innovation in the sulfuric acid market since the 1920s, MECS remains the industry leader in technology, engineering and equipment dedicated to sulfuric acid producer’s needs. Major sulfuric acid plants worldwide have

* Corresponding author. Tel.: +32 2 658 26 53 E-mail address: [email protected]

1877-7058 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of SYMPHOS 2015

doi:10.1016/j.proeng.2016.02.077

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Sarah Richardson et al. / Procedia Engineering 138 (2016) 199 – 205

installed MECS® Catalyst and have benefited from the technical developments offered by MECS over the years. With a comprehensive understanding of sulfuric acid plants, MECS product innovations and customer service offerings continue to provide benefits far beyond that of catalyst. This paper will focus on the innovative developments in the MECS® Catalyst product portfolio and provide case study documentation of these benefits. Sulfuric acid catalyst history began with platinum-based catalysts which were expensive, unreliable, and easily poisoned. Through a partnership in research & development between various independent entities and corporations (to include MECS), a new vanadium-based catalyst formula was developed. The first installation of MECS® Catalyst occurred in 1925 when a vanadium-based, pellet-shaped catalyst was shipped to the Monsanto Chemical Works plant in Sauget, Illinois. This catalyst remained the industry standard until the 1960s, when MECS developed and introduced a new formula of catalyst designed specifically for the low SO2 and kinetically-hindered conditions located in beds 3 and 4 of the standard sulfuric acid plant converter. The new catalyst provided higher activity per unit volume with the identical catalyst dimensions and resulting pressure drop of the existing catalyst. The advent of this new catalyst formula in the early 1960s marked a major improvement in the overall acid plant process.

Figure 1: MECS® Sulfuric Acid Catalyst Research Laboratories, circa 1950s (a) and present (b)

Due to major societal concerns regarding the environment and energy consumption in the 1970s, the industry began to focus on technology and products that could respond to these challenges. MECS offered a catalyst solution in the form of a larger diameter pellet and then a new type of catalyst shape, called a “Raschig” ring. These catalysts lowered pressure drop across the converter and provided higher activity. In addition, MECS focused on reducing acid plant costs by developing more robust catalysts offering lower screening losses. The 1990s saw an increased need for production efficiency and reduced SO 2 emissions. MECS responded to these needs with the introduction of a cesium-promoted catalyst, which took advantage of the low temperature properties of the cesium promoter. This catalyst generated excellent SO2 conversion at bed inlet temperatures from 30 to 40°C lower than conventional catalysts. The low temperature activation allowed for new acid plant designs with dramatically lower SO2 emissions as well as improving the conversion performance of existing double and single absorption acid plants. MECS® Catalyst Research and Development continued to innovate in the form of shape modifications and formula enhancements. Ribbed ring catalysts, with much lower pressure drop characteristics, as well as increased activity offered by a larger surface area, were developed for both the vanadium-based and cesium-promoted catalyst formulas. The ribbed ring products quickly became the industry standard due to their high performance and low pressure drop. With these introductions, MECS offered sulfuric acid plant producers a strong portfolio of catalyst products with benefits applicable for a multitude of operating requirements.


Figure 2: MECS® Catalyst Shapes, left to right, GEAR® hexa-lobed ring, XLP ribbed ring, LP ring, and Pellet

With a continued focus on energy savings and performance improvement, MECS expanded their catalyst portfolio yet again in 2011. MECS is the only catalyst manufacturer to offer GEAR® Catalyst utilizing a unique hexa-lobed ring shape which, combined with an improved catalyst formula, has demonstrated better conversion performance, lower pressure drop and improved dust handling. By geometrically optimizing the catalyst shape, GEAR® Catalyst offers more surface area for access to active sites than any other catalyst on the market. In addition, when loaded into a catalyst bed, the hexa-lobed ring shape creates a catalyst bed configuration which increases spacing between the catalyst rings, lowering pressure drop significantly over other manufacturer’s catalyst. Compared to standard ribbed ring or daisy-shaped catalyst, GR-330 GEAR® Catalyst offers approximately 10 to 15% lower pressure drop at plant start-up (clean pressure drop). As the plant continues to operate, dust accumulates in the upper passes, creating the possibility of increased pressure drop across the converter. The unique hexa-lobed ring shape provides superior dust handling capability; thus, over time, the pressure drop benefits expand, reaching a potential of approximately 30% less pressure drop after 24 months of service. This typically translates into between two to six months of extended operating time before the system pressure drop reaches the plant blower limit. The extended production campaign offers savings to sulfuric acid plants including extended plant up-time, increased acid production, lower catalyst replacement costs, and lower maintenance and operating costs.

Figure 3: Lower Pass 1 Pressure Drop over Time with GEAR® Catalyst

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Lower operating costs can be illustrated in the energy savings estimated realized by various acid plant types. A typical 200 MTPD spent acid regeneration plant (SAR), using GEAR® Catalyst in place of daisy-shaped catalyst in pass one, over a two year screening schedule, can save over $2000 USD per year, which equates to more than $4000 USD over the two year turnaround cycle. A much larger typical sulfur burning plant of 2000 MTPD could save over $17,000 USD per year with close to $35,000 USD of estimated savings over the two year screening cycle. Finally, a typical metallurgical sulfuric acid plant producing 3500 MTPD can expect to save almost $60,000 USD over the two year cycle. All of these calculations are based on an estimated 10 US cents per kilowatt hour electricity cost. Table 1: Pass 1 Energy Savings Case Study, GR-330 vs. Daisy-Shaped Catalyst Plant Type

Plant Size

Estimated Energy Savings (USD/yr)

Spent Acid Regeneration

200 MTPD

$2200

Sulfur Burning

2000 MTPD

$17000

Metallurgical

3500 MTPD

$28000

These benefits are currently being enjoyed by the Fluorsid II Sulfuric Acid Plant in Italy. This plant selected GEAR® Catalyst with Super Cesium SCX-2000 in the final pass for their recent new plant designed by MECS. After a smooth start-up in 2013, MECS technicians visited the plant to perform a PeGASyS (MECS proprietary Portable Gas Analysis System) test, to evaluate the plant performance on a pass-by-pass basis. At Fluorsid, the PeGASyS test demonstrated that the GEAR® Catalyst pressure drop after 10 months of service was lower than typical daisy-shaped catalyst at clean pressure drop. Pass 1 showed no pressure drop build-up after 10 months of operation. Table 2: Fluorsid II Converter Pressure Drop Data Start-Up (August 2013)

Start-Up Values Normalized

PeGASyS (June 2014)

Plant Rate (MTPD)

411

448

448

Inlet SO2 (%)

11

10.95

10.95

Pass 1 dP (mm w.c.)

90

105

102

Pass 2 dP (mm w.c.)

70

82

92

Pass 3 dP (mm w.c.)

105

123

133

Pass 4 dP (mm w.c.)

90

105

122

Total dP (mm w.c.)

355

414

449

2. Innovative New Product Introductions An interesting extension of the unique GEAR® Catalyst benefits is offered for customers who would benefit from combining the low temperature benefits of cesium-promoted catalysts with a GEAR® catalyst shape. An example would be an existing acid plant with the following challenges: x High dust contamination in the gas stream (such as metallurgical plants or sulfur burning plants with varying quality of sulfur in the feed) or x Desire to increase throughput without increasing pressure drop or emissions The demonstrated superior dust handling provided by the hexa-lobed ring shape of the GEAR® Catalyst, especially in pass 1, inspired the addition of GEAR® cesium catalyst, GR-Cs, to the MECS® Catalyst portfolio. Sulfuric acid plant converters operating with lower bed inlet temperatures have the opportunity to upgrade to GEAR® cesium catalyst for energy savings and excellent dust handling. Increasing throughput in an existing plant is often a balance, requiring the process engineer to decide whether additional production is worth the higher energy cost or additional emissions. In many cases, blower capacity or plant emissions permit levels can limit the plant’s ability to achieve increased output. With the GEAR® cesium catalyst, GR-Cs, as a replacement for vanadium catalyst, a plant can increase converter performance while limiting additional emissions or avoiding excessive load on the blower.


Figure 4: GEAR® GR-Cs Catalyst

The most recent product enhancement developed by MECS® Catalyst Research and Development is a minor, but high activity boosting modification to the well-established Super Cesium SCX-2000 cesium catalyst formula. This proprietary formula improvement positively affected the SCX-2000 cesium catalyst activity, offering customers higher performance in the fourth and fifth converter passes. The improved formula SCX cesium catalyst allows a customer to achieve lower SO2 emissions through higher catalyst activity and better conversion or the ability to operate at a lower bed inlet temperature of 385°C. A laboratory case study illustrates the advantages of improved formula super cesium catalyst. Extensive lab data on improved formula SCX indicates that it will accomplish the same SO 2 emissions with less catalyst required, equaling a reduction of approximately 10 liters less SCX catalyst per ton of acid produced. In this way, the customer can save on catalyst costs. If lower emissions are preferred, lab data confirms that, based on the same process conditions as above, improved formula SCX will accomplish approximately 80 ppm less SO2 emissions than the former SCX formula at the same catalyst loading. Actual results depend on specific plant conditions.

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Figure 5: Improved Performance of SCX-2000 Super Cesium Catalyst

The new formula SCX cesium catalyst is available to MECS sulfuric acid catalyst customers now. Installation in two test cases is scheduled in 2015. These test cases will confirm the additional catalyst activity in an actual plant environment and both cases allow comparison directly with existing cesium-promoted catalyst. When available, test case results can be obtained by contacting the authors. 3. Proven MECS® Catalyst Excellence – Client Case Studies The GEAR® and SCX-2000 innovations join the rest of the MECS portfolio offering catalyst solutions to major sulfuric acid producers placing their confidence in MECS technology and know-how. The sulfuric acid industry catalyst workhorse is the MECS® XLP catalyst, a vanadium-based catalyst installed in hundreds of plants worldwide. MECS is unique in proving that XLP and GEAR® are sulfuric acid catalysts that can be applied in all passes, thus simplifying maintenance complexity, reducing inventory costs, and increasing flexibility for unexpected replacement requirements for all standard (XLP) and high performance (GEAR® series) applications. In applications where the use of cesium-promoted catalyst offers the activity and performance needed to achieve more activity with less catalyst, producers rely on MECS® Cesium Catalysts, especially the improved formula Super Cesium SCX2000. Many years of reliable catalyst performance, excellent sales support, and confidence in MECS technology influenced PCS Phosphate Company, Inc. in Aurora, North Carolina to load only MECS® Catalyst into their new mega-sized sulfur burning plant project, Plant No. 7, which started up in 2010. When PCS Phosphate Aurora, a subsidiary of fertilizer giant Potash Corporation of Saskatchewan Inc., launched their 4082 MTPD (4500 STPD) sulfuric acid plant project, they knew it would be the largest in North America. They chose MECS to do the design and installed MECS proprietary equipment such as a ZeCor® Final Tower, UniFlo® Acid Distributors, Brink® Mist Eliminators, and MECS® Catalyst. In addition, they selected a design with the MECS® Heat Recovery System (HRS™) technology, increasing steam generation and efficiency as well as lowering operating costs. For example, using the steam recovered from the sulfuric acid process saves the cost of coal that would have been burned on-site to produce electricity and reduces PCS Aurora’s carbon footprint by 800,000 tons per year. Another environmental benefit was achieved with the MECS® Catalyst installed in this large sulfuric acid plant project. As the size of sulfuric acid plant projects increases, these large plants and resulting large converters offer


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challenges such as effective gas distribution, SO3 removal and SO 2 emissions. Because of MECS’ extensive design experience and practical sulfuric acid plant knowledge, MECS is a preferred partner for these mega-projects, with over 30 plants designed exceeding 3000 MTPD sulfuric acid production. With an in-depth understanding of the challenges of large scale converter design, MECS is able to provide the most efficient combination of converter engineering and catalyst selection to customers. In the case of PCS Phosphates in Aurora, the standard catalyst combined with SCX-2000 in the final pass offered low pressure drop and high conversion. Measured SO 2 emissions were 75% of the maximum allowable level at 105% of the sulfuric acid plant design capacity. Not only was the plant able to run higher production than name plate, but SO2 emissions were well below the requirement. Table 3: PCS Aurora Plant No. 7 Performance Results Design

Demonstrated

Plant Capacity

4082 MTPD

4282 MTPD

SO2 Emissions

1.00 kg/MTPD

0.725 kg/MTPD

Low SO2 emissions and higher production than name plate were also design criteria for the Fluorsid II Plant mentioned earlier in this paper. Fluorsid returned to MECS for their new plant design after successfully operating Fluorsid I with MECS® Sulfuric Acid Technology for several years. For Fluorsid II, the company wanted to maximize acid production, minimize SO2 emissions, and reduce capital expenditures by reusing the Plant I converter design. This requirement meant that there was no flexibility to add converter passes or additional catalyst in the new plant. In order to achieve higher production and lower emissions with a set converter size and fixed catalyst volumes, MECS knew that Fluorsid II needed high performance catalyst. The premium GEAR® Catalyst combined with high-activity Super Cesium SCX-2000 catalyst offered exactly the required characteristics to meet Fluorsid’s stringent design criteria. Specifically, Fluorsid requested that MECS offer them the ability to produce 10% more sulfuric acid than the design capacity. After optimizing the catalyst design using the same converter specifications as the previous plant, MECS was satisfied and Fluorsid was delighted when they were able to run at 110% of design capacity with low pressure drop. The Fluorsid SO2 stack analyzers showed lower SO2 emissions than permitted, thus illustrating the ability of MECS to meet customer’s unique design challenges. 4. Summary MECS is known for its proven sulfuric acid catalyst portfolio and catalyst designs based on practical experience and extensive plant knowledge. But, MECS offers the client more than just catalyst. MECS offers world-class knowledge of sulfuric acid, innovative technologies and proprietary products for the entire acid plant. Local, personalized service and technical services are also offered for troubleshooting, maintenance, training, and optimization, as well as maintenance planning support. MECS offers everything the client needs to achieve optimal sulfuric acid plant performance. Copyright © 2015 MECS, Inc. All rights reserved. The DuPont Oval Logo, DuPont™, The Miracles of Science™ and all products denoted with a ® or ™ are trademarks or registered trademarks of E. I. du Pont de Nemours and Company or its affiliates.