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MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

Benjamin Wood, Miklos Lengyel and Cristina Kulczycki

Operating data from Mexicana de Cobre’s La Caridad sulphuric acid plant was used to study the ability of MECS® GEAR® catalyst to reduce pressure-drop during the treatment of acid gas from copper smelters

Introduction

MECS® catalyst for sulphuric acid production is part of the DuPont Clean Technologies (DuPont) portfolio and has been manufactured since the 1920s. In 2011, DuPont introduced the MECS® GEAR® line of catalysts. GEAR® catalysts feature a hexa-lobed ring structure (Figure 1). This structure increases the void space between catalyst rings, decreasing pressure drop and improving dust handling. Additionally, the improved formulation of GEAR® results in higher activity.

In 2015, Mexicana de Cobre elected to replace its existing ribbed catalyst with GEAR® catalyst in the first three passes of its catalytic converters at its La Caridad sulphuric acid plant. Operational data from the plant shows that the open structure of GEAR® significantly decreases pressure drop through the catalyst bed while improving upon overall conversion. This article explains how this was achieved.

Figure 1: GEAR® hexa-lobed ring shape.
MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

Impact of GEAR® Shape on Dust Distribution within a Catalyst Bed

During the operation of sulphuric acid plants, a fraction of the acid gas sent to the catalytic converter is composed of particulate matter. The primary sources of this particulate matter are the ash content in the raw material that is combusted to form SO2, and dust in the unfiltered air of combustion. During operation of sulphuric acid plants, the particulate matter is typically captured by the first pass in the catalytic converter. The accumulation of this dust results in increasing pressure drop through the pass, eventually requiring shut-down of the plant and catalyst screening once the pressure drop has exceeded the maximum allowable by the process blower. Frequent downtime and catalyst screening entail significant costs for acid producers.

Figure 2: Sleeves used in dust distribution study.
MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

As dust accumulates in the catalyst bed, it is important that it does not accumulate solely in the front of the bed, as this would lead to rapid build-up of flow restrictions in the void spaces between catalyst particles. Instead, it is preferable that dust accumulates throughout the entire catalyst bed in order to avoid a high level of flow restriction at any single depth of the bed. Proper catalyst-shape design can facilitate even dust distribution. Compared to standard ribbed ring catalysts, GEAR® catalyst demonstrates improved dust distribution. This is due to the unique hexa-lobed ring shape, which increases the void space in the catalyst bed, allowing dust to penetrate farther into the catalyst bed.

In order to demonstrate the superior dust handling capabilities of GEAR® catalyst, a test was performed at a MECS® sulphur-burning sulphuric acid plant, in which sleeves (see Figure 2) containing about 200 litres of catalyst were inserted into a catalyst bed. After three years, the sleeves were removed from the bed, and the amount of dust was quantified at various bed depths. The results are shown in Figure 3.

Figure 3: Comparison of dust distribution in ribbed and GEAR® catalyst beds after three years of operation.
MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

As shown in Figure 3, nearly 70 per cent of the dust accumulated in the top third of the sleeve containing ribbed catalyst. In comparison, a little less than 40 per cent of the dust accumulated in the top third of the sleeve containing GEAR® catalyst with the remaining dust distributed on a fairly even basis across the bottom two thirds of the sleeve.

Performance Data at Mexicana de Cobre’s La Caridad Sulphuric Acid Plant

Mexicana de Cobre is part of Grupo Mexico. The La Caridad facility is located in Sonora, Mexico. Mexicana de Cobre operates two sulphuric acid plants at the La Caridad site, which treat acid gas produced during copper smelting. In 2015, Mexicana de Cobre’s La Caridad sulphuric acid plant replaced the catalyst in the first three passes of one of their catalytic converters. Before replacement, all four catalyst passes contained ribbed catalysts, as shown in Table 1, with passes 1 and 4 including caps of cesium-containing ribbed catalyst to facilitate light-off. After replacement, the first three passes contained GEAR® catalyst, with the first pass including a cap of cesium-containing GEAR®. The fourth pass was not replaced, still containing ribbed catalyst with a cap of cesium-containing ribbed catalyst.

Table 1: Bed pressure drop before and after replacement with GEAR® catalyst. Expand
MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

As shown in Table 1, before catalyst replacement, when each of the beds consisted of ribbed catalysts, the pressure drop in passes 1-4 was 340, 299, 336, and 136 mm wc, respectively. After catalyst replacement with GEAR® catalyst, the pressure drop in passes 1-3, while maintaining the same operating capacity and catalyst bed volumes, was 95, 82, and 95 mm wc, corresponding to pressure drop decreases of around 72% in each bed. The fourth pass, which was not replaced, showed a slight increase in pressure drop from 136 to 163 mmWc, or 20%. In addition to the improvements in pressure drop, the outlet concentration of SO2 decreased from 635 ppm to 345 ppm. These results demonstrate the dramatic improvements in pressure drop resulting from the GEAR® shape.

MECS® GEAR® catalyst demonstrates superior dust capture and pressure drop performance at metallurgical sulphuric acid plant

Acknowledgements

The authors are grateful to Mexicana de Cobre’s plant manager, Francisco Rubio for providing plant operation data. The authors would also like to thank Oscar Matus, DuPont Clean Technologies long time representative in Mexico, and owner of OMATUS. Finally, the authors would like to acknowledge the technical contributions of Lonita Blackman, Timothy Felthouse, Gerald Hook, and Carmo Peraira.

In a box:

Mexicana de Cobre’s La Caridad Sulphuric Acid Plant

Mexicana de Cobre is part of GrupoMexico. The La Caridad facility is located in Sonora, Mexico. Mexicana de Cobre operates two sulphuric acid plants at the La Caridad site, utilizing acid gas produced during copper smelting.

About DuPont Clean Technologies

DuPont Clean Technologies applies real-world experience, history of innovation, problem-solving success and strong brands to help organizations operate safely and with the highest level of performance, reliability, energy efficiency and environmental integrity. The Clean Technologies portfolio includes STRATCO® alkylation technology for production of clean, high-octane gasoline; IsoTherming® hydroprocessing technology for desulphurization of motor fuels; MECS® sulphuric acid production and regeneration technologies; BELCO® air quality control systems for FCC flue gas scrubbing and other refinery scrubbing applications; MECS® DynaWave® technology for sulphur recovery tail gas-treating solutions; and a comprehensive suite of aftermarket service and solutions offerings. Learn more about DuPont Clean Technologies at http://www.cleantechnologies.dupont.com.

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