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By Shell Catalysts & Technologies on Jul 11, 2022

Waste-to-energy (WTE) production is a growing trend among global energy producers. WTE, or the conversion of wet, solid or gaseous waste feedstocks into energy, can increase sustainability by providing circular economy solutions.

Shell Catalysts & Technologies is also involved in evolving today’s WTE solutions. For more than 40 years, we have developed and evolved catalysts that efficiently convert biowaste into valuable transportation fuels. For the development of our next-generation biofuels technology IH², our researchers have filed 28 processes and catalysts patents. IH² is a technology intended to take organic waste and convert it into lower-carbon transportation fuels such as petrol, diesel and jet fuel.

While waste-to-energy plant operators seek to repurpose waste into energy to promote sustainability, one of their primary concerns is managing air pollution. Often, air pollution control dominates the overall design of waste-to-energy plants. Some of these solutions, like Shell Catalysts & Technologies’ Selective Catalytic Reduction (SCR): DeNOx System also known as Shell DeNOx System (SDS) and Shell Dioxin Destruction System (SDDS) reduces air pollutants from WTE production in similar, proven methods as in the past for traditional refineries.

What is the impact of nitrogen oxides (NOx) on air pollution?

Concerns around NOx emissions, which are gases formed when “fuel is burned at high temperatures� by industrial sources like “power plants, industrial boilers, cement kilns and turbines� as well as automobiles, trucks and other vehicles, began in the United States in the early 1960s.1

The increase of industry and of transportation all over the world created more pollutants in the air. For humans, air with a high nitrogen dioxide (NO2) concentration can lead to respiratory problems such as asthma, coughing, wheezing, difficulty breathing and infections.

Environmentally, the rapid increase in energy produced by fossil fuels had contributed to the rise of NOx emissions in the atmosphere, which resulted in acid rain. Acid rain is created when NOx interacts with water, oxygen and other atmospheric chemicals. This can damage forests and water bodies. Additionally, this type of pollution has an impact on air quality, making it not only unsafe to breathe, but making it hazy and lowering visability.

The Clean Air Act of 1963 set forth “federal research aid, urged development of state control agencies and involved the federal government in inter-state pollution issues.â€�2 The legislation was amended in 1965 to require the U.S. Department of Health, Education and Services to create and enforce auto emissions standards. Federal lawmakers amended the legislation several more times, including in 1990. At that time, the law changed to mandate decreases in gas emissions to control acid rain. It also increased regulations on toxic pollutants such as NOx emissions.

Explore: How CANSOLV amine technology was developed to address air pollution concerns

Reducing NOx emissions with Shell’s Selective Catalytic Reduction (SCR) System

To help refineries meet mandates to reduce NOx, dioxins and other harmful emissions pollutants, Shell commercialised Shell DeNOx System (SDS) catalyst technology. SDS provides reliable technology for Selective Catalytic Reduction (SCR) of NOx from stationary and mobile combustion sources and chemical processes. Proven around the world, SDS catalyst technology is unique in its ability to provide high NOx reduction across a broad range of conditions.

The SCR system is based on a lateral flow reactor (LFR) design, which allows for low-temperature activity and extremely low-pressure drop. The SCR system adds ammonia (NH₃) to flue gas containing NOx. The flue gas/NOx mixture then passes over an active catalyst resulting in a conversion of nitrogen oxides (NO and NO₂) to nitrogen (N₂) and water (H₂O), thus reducing NOx.

Another solution to aid in the removal of dioxins is the Shell Dioxin Destruction System (SDDS). The SDDS system provides for the catalytic destruction of dioxins and furans from municipal solid and hazardous waste incineration facilities. Using SDDS allows for high conversion of dioxin at a lower operating temperature with low-pressure drop across the LFR. As a result, production impact is lessened.

SDDS allows for less complicated retrofits. Installation at the end of the process can result in cost savings around installation and operating costs.

The SCR and SDDS systems have helped energy producers meet mandates to reduce pollutants in emissions, achieve performance requirements and reduce energy consumption. At low temperatures, the two systems outperform other catalyst systems, making either a highly cost-effective retrofit for existing facilities where exhaust temperatures are low.

How waste-to-energy plants reduce NOx emissions with the SCR system

In waste-to-energy plants, NOx emissions come from waste combustion and exist in the flue gas. SDS is unique because the technology can provide high NOx reduction in various applications. Those include:

• Boilers/turbines;
• Furnaces/heaters;
• Waste incineration/biomass; and
• Nitric acid plants & chemical processes.

For example, if a customer burns natural gas through a boiler to produce steam, the combustion reaction will inevitably generate NOx. If installed before the emission point or stack, SDS can meet the customer’s emission performance requirement with no supplemental heating and less energy consumption.

To reduce NOx emissions, the SCR system is incorporated with Shell Catalysts & Technologies’ DeNOx catalysts. The DeNOx catalysts presents high NOx removal capability at low temperatures, allowing SDS integration at the end of flue gas treatment systems on waste-to-energy (WTE) plants with minimal or no flue-gas reheat.

The potential benefits include increased energy efficiency and optimised productivity. In WTE and petrochemical industries, operators’ investments to reduce NOx emissions include their goal to decrease energy consumption, thereby leading to cost savings and lower carbon footprint.

Explore pathways to adapt to the energy transition

Learning to navigate emissions reduction

Energy producers must meet growing demands while simultaneously decreasing the environmental impact and meeting environmental protection regulations. As such, energy producers are investing in technologies that address every facet of the challenge.

Shell Catalysts & Technologies offers solutions and processes to help energy producers plan for increased energy demand over time and limit harmful emissions that impact the environment. The Shell DeNOx System, once installed and implemented, can help reduce emissions, especially for the increasing number of waste-to-energy plants. The technology also has the potential to reduce energy producers' cost as they continue to build strategies toward decarbonisation.

¹ _{“Nitrogen Oxides (NOx) Control Regulationsâ€�, United States Environmental Protection Agency, 28 March 2022, https://www3.epa.gov/region1/airquality/nox.html.}
² _{Clean Air Act, US Legal, accessed 17 June 2022, https://environmentallaw.uslegal.com/federal-laws/clean-air-act/.}