Embracing ESP Technology

The cement and lime industries are experiencing increased environmental concern regarding carbon dioxide emissions. This will likely drive the installation of CO₂ scrubbers at kilns in both sectors. Recent experience with CO₂ scrubbers in other industries has demonstrated the importance of the cleanliness of the gases entering a scrubber system. In particular, solid and liquid particles such as sulfuric acid mist will cause problems such as excessive reagent consumption and equipment fouling. This article will describe the potential of wet electrostatic precipitators to significantly reduce the particulate load at the inlet to a CO₂ scrubber to minimise reagent consumption and maintenance problems at the downstream scrubber.

Introduction

There is a rapidly growing interest in technologies to abate CO₂ emissions worldwide. Reductions in current rates of carbon dioxide emissions from existing sources are becoming a pillar of the world’s strategy to reduce the greenhouse gas concentration in the atmosphere. This strategy is particularly relevant to the cement industry because of the nature of the process, which involves both the combustion of fossil fuels and the conversion of calcium carbonate to calcium oxide by separating the CO₂ molecule.

Much of the attention directed towards CO₂ emission abatement is focused on CO₂ scrubbing technologies. Such technologies are well developed. Most use amines to absorb CO₂ and then regenerate the amine solution to yield a concentrated stream of nearly pure CO₂ gas which can then be reused or permanently sequestered. Such CO₂ scrubbing systems work best when the incoming gases are free of undesirable impurities. Thus, cleaning the incoming gases is essential to the overall CO₂ emissions control process. This article will address the use of wet electrostatic precipitation systems to affect this inlet gas cleaning step.

Industry background

The cement and lime industries are responsible for about 8% of global CO₂ emissions. In 2021, these industries emitted an estimated 2.9 billion t of CO₂. This is more than the CO₂ emissions from worldwide aviation or the entire European Union. The primary source of CO₂ emissions from the cement industry is the production of clinker which is the main ingredient in cement; for the lime industry it is the calcination of limestone.

The other primary source of CO₂ emissions from the cement and lime industries is the combustion of fuels to heat the kilns.

This accounts for about one-third of the total emissions. There are 99 cement plants in the US. There are 96 operating kilns in the lime industry, with another 177 lime kilns in the pulp and paper industry. Given these facts, it is no surprise that the cement and lime industries are the second largest CO₂-emitting industry behind electric power generation. Clearly, the industry faces a significant challenge.

CO₂ scrubbers

The most widely applied CO₂ scrubbing technology uses an aqueous-monoethanolamine (MEA) solution to absorb dilute CO₂ and render it into a concentrated form after desorption. The concentrated CO₂ stream is then suitable for sequestration, enhanced oil recovery, or other industrial uses. There are many full-scale CO₂ scrubbers of this type in operation, and they have been shown to reduce CO₂ emissions from flue gases by more than 90%. While there are also several other processes in various stages of development, the MEA scrubbing process appears to be the most widely accepted. There is little question that this technology is mature and proven effective.

However, while the MEA CO₂ scrubbing process is proven, it is also costly to operate. There is much work involved in minimising OPEX for these scrubbers. Still, even under the best conditions, an MEA scrubbing system could consume up to 30% of the power of an upstream coal-fired generating station. One of the main OPEX factors is solvent loss, and a contributing factor to solvent loss is the presence of contaminants in the inlet gas stream.

Reported experience also shows that the cleanliness of the inlet gas stream is essential in minimising maintenance costs. Solid particulate matter in the incoming gas stream can foul equipment such as heat exchangers in the scrubbing system.

These contaminants can be solid and/or liquid particles that form when the inlet gas stream is cooled by saturation before contact with the CO₂ absorbing solution. Of particular concern is the sulfuric acid mist that forms in this way.

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Read the article online at: https://www.worldcement.com/special-reports/20102023/embracing-esp-technology/