Electric Furnace Gas Cleaning Solutions Amidst Increasing Environmental Requirements

What does this mean specifically for the Smelting industry? Increasingly tighter emission limits.

In smelting plants, the main emission sources are electric furnaces. The smelting process goes as follows: The furnace generates CO-rich dust-laden off-gas, which is then extracted from the furnace straight to the gas handling and cleaning system, and then finally, into the atmosphere.

The new demand for electric furnace gas handling systems must not compromise the safety or reliability of the product. So the challenge remains: Is there an econominically feasible solution for meeting both environmental and technological requirements?

Requirements for Electric Furnace Gas Cleaning

Smelting reduction reactions generate CO-gas as a byproduct due to the lack of oxygen in the process. This is because CO-rich off-gas is toxic and explosive when mixed with oxygen. Off-gas temperatures are also very high, at times reaching over 1000 degrees celsius. In addition to CO-gas, other harmful components (such as sulfur compouds, nitrogen oxides, chlorides, fluorides and mercury) may be present in the off-gas atmosphere depending on the furnace feed materials.

Considering these issues, conditions for gas cleaning are quite unique, and have strictly imposed technological demands.

The most important requirement for electric furnace gas cleaning is safety. Due to the risk of explosion when mixing CO-gas and oxygen, each gas handling system needs to be designed extra tight in order to eliminate air ingress during the process. Thus, systems operating on overpressure are preferred over under pressure systems.

High availability and reliability are also required from gas cleaning solutions. The operation of furnaces needs to be stable, and any gas handling system cannot compromise this. Therefore, gas cleaning solutions need to be unwaveringly robust whilst requiring little maintenance. With this, investment and operating costs need to remain reasonable.

The most topical qualification for gas cleaning at the moment is, of course, the important environmental concern. Gas cleaning systems need to meet emission limits set by officials, legislations and regulations, all whilst remaining effective and efficient.

Metso Outotec Provides Solutions

Here at Metso Outotec, our gas handling portfolio is exceedingly extensive. We supply products and solutions for several different processes and needs, such as: Gas cleaning and cooling for both particulate and gaseous emissions, off-gas incineration, wet and dry gas handling, hot gas quenching, and so much more.

Gas handling conditions in electric furnaces are especially challenging due to the high temperatures as well as the toxic and explosive CO-gas. Fortunately, our products are specifically designed for the unique conditions and requirements of closed electric furnace applications.

Outotec Venturi Scrubber

The Outotec Venturi Scrubber is a widely known and utilised product within the Smelting industry. With its proven track record of being a high-pressure scrubber, the product allows for safe and effective cleaning of any harmful or explosive process gases.

The scrubber inhales furnace off-gases and produces overpressure to the gas line. This overpressure prevents air from entering the line, thus enabling safer handling of CO gas. In addition to cleaning, the scrubber also cools the gas and quenches the sparks – further eliminating any risk of explosion.

The Outotec Venturi Scrubbers clean off-gases in two stages: the primary venturi and secondary venturi. High-pressure water is sprayed into venturi tubes which allows for particles in the gas to collide and attach with water droplots. At the same time, high-pressure water jets cool and pressurize the gas. There is an effective droplet separator that then removes the droplets and particles from the gas flow, thus allowing clean gas flow to the gas line.

This product is specifically designed for maximising safety and ease of operation. Each detail is intended to prevent the risk of explosion and air ingress to the system. The Scrubber also has the capability to handle variating gas flows without adjusting the scrubber operation. Due to the lack of moving parts, this also allows for low maintenance.

Outotec CO gas filter

Metso Outotec understands that at times, an even more efficient gas cleaning technology is required. Collecting the finest particles from off-gases is challenging with wet scrubbing methods – which is why we have developed a filter specifically designed for efficient removal of the smallest particles for CO-gas applications. When combined with the Outotec Venturi Scrubber, there is no issue with achieving those ultra low emissions.

Along with a modular design and an easy installation, the Outotec CO-gas filter is also designed for maximum safety. Safe CO-gas handling is extremely important, and this cassette-type filter eliminates the multiple risks associated with handling carbon monoxide gases. The air ingress is prevented using water lock tanks, sealing and nitrogen jets. In addition to this, filtered gas is very clean, thus enabling the CO-gas to convert into numerous different solutions, such as cogeneration and a replacement of fossil fuels.

Moving Forward in the Industry

With the concern for environmental issues growing, the future of Smelting is bound to bring increasingly tighter environmental requirements. Continuous improvement and development is absolutely crucial in this day and age. Therefore, utilising CO-gas for electricity production and replacing fossil fuels allows for both environmental and economic benefits for your operation.

Metso Outotec’s product portfolio and project execution provides solutions for both present and future needs. Our reliability in meeting ultra-low environmental targets has been proven, as over 170 references from around the world are utilising our electric furnace and CO-gas applications.

With emission limits tightening, having maximum efficiency in gas cleaning solutions is becoming an essential. This is why we continuously develop our products to meet the future environmental targets whilst providing cleaner technologies. The need to apply new technologies to smelting furnaces is vastly approaching, and here at Metso Outotec, we are happy to be ahead of the curve.

For more information regarding Metso Outotec gas cleaning solutions, you can watch our webinar ”Electric Furnace Gas Cleaning Solutions in Tightening Environmental Requirements." Listen to our industry experts discuss environmental requirements, solutions, success stories, as well as what the future holds within the Smelting Industry.

This article is part of our Smelting Newsletter Issue 1/2020. Visit the issue front page for all articles and greetings from Jyrki Makkonen, Vice President of Smelting business line.