By Published On: July 8, 2024Categories: Library

Air pollution control systems have undergone a remarkable transformation over the past few decades, driven by stricter regulations, technological advancements, and a growing public demand for cleaner air. The wood products industry, which once had minimal emission controls, exemplifies this transformation, spurred by advancements in air pollution control technologies to meet stringent standards. This article takes a deep dive into the history of air pollution control, tracing its evolution from rudimentary beginnings to the sophisticated systems of today, and provides insights into future trends, by using the wood products industry as a backdrop.

Rudimentary Beginnings – Minimal Emission Oversight In The Early Days of Air Pollution Control

To truly appreciate the strides made in air pollution control, we must understand the historical context of the wood products industry. Though a relatively young sector originating in the late 19th and 20th centuries, it quickly made a significant impact on air quality. The drying of wood for products like plywood, particleboard, and oriented strand board (OSB) generated substantial emissions, culminating in an era notoriously known as the “blue haze.”

The “Blue Haze” Era

Prior to the 1970s, emission controls for wood dryers were minimal, with typical outlet emissions reaching alarmingly high levels of particulate matter (0.1 gr/scfd or 228 mg/Nm3), volatile organic compounds (VOCs) (0% efficiency), and hazardous air pollutants (HAPs) (0% efficiency). The rudimentary air pollution control measures employed at the time included:

  • Gravel bed filters which used a bed of gravel to capture particulate matter.
  • Ionizing wet scrubbers that used electrical fields to ionize particles, making them easier to capture in a scrubbing liquid.
  • Low-energy wet scrubbers that used a liquid spray or stream to remove particulate matter from the gas stream.

These methods proved inadequate in mitigating these emissions, with most of the captured emissions often being used as combustion air for on-site boilers. As a result, a pervasive blue haze enveloped mill towns across the western and southeastern regions of the United States, serving as a visible manifestation of the industry’s substantial environmental footprint.

The Clean Air Act’s Impact On Air Pollution Control Systems

The Clean Air Act of 1970 marked a pivotal turning point in air pollution control. Driven by growing public demand for cleaner air, this landmark legislation established the Environmental Protection Agency (EPA) and set ambient air quality standards alongside emission limits for major stationary sources, new sources, and mobile sources. Subsequent amendments in 1977 and 1990 further expanded limits for air toxics and introduced new requirements, propelling the wood products industry to adapt and develop more innovative technologies like Wet ESPs and RTOS, in order to meet the increasingly stringent regulations.

The Technical Leap – Wet Electrostatic Precipitators and Thermal Oxidizers

The wood products industry responded to the Clean Air Act with a wave of technological innovations over the next two decades.

The 1980s Introduces Wet ESPs

The 1980s marked a significant milestone in air pollution control systems with the introduction, widespread adoption, and installation of wet electrostatic precipitators (ESPs) for particleboard and oriented strand board (OBS) dryers. These wet ESPs quickly became recognized as the Best Available Control Technology (BACT) for particulate matter emissions in many regions across the United States.

The 1990s – Thermal Oxidizers Take Center Stage

The amendments to the Clean Air Act in the 1990s greatly expanded emission limits for air toxics, including volatile organic compounds (VOCs). To comply with these tightening regulations, the wood product industry turned to thermal oxidation systems as a solution for VOC control. Specifically:

1. Regenerative Thermal Oxidizers (RTOs). The “Tier 1 consent decrees requiring VOC controls” in the 1990-1995 period led to the first installations of regenerative thermal oxidizers (RTOs) on oriented strand board (OSB) dryers. RTOs use a regenerative thermal oxidation process to destroy VOCs, capturing and reusing the heat from the oxidation reaction to improve energy efficiency.

2. Regenerative Catalytic Oxidizers (RCOs). During this same period, the first regenerative catalytic oxidizers (RCOs) were implemented on veneer dryers. RCOs employ a catalytic oxidation process to oxidize VOCs at lower temperatures compared to traditional thermal oxidizers, further enhancing energy efficiency.

3. Combined Wet ESP/RTO Systems. By the late 1990s, the industry had developed combined wet electrostatic precipitator (ESP)/RTO systems specifically for OSB dryers. These integrated systems leveraged the strengths of both technologies, with wet ESPs effectively controlling particulate matter emissions and RTOs addressing VOC emissions.

The widespread adoption of thermal oxidation systems, including RTOs and RCOs, during the 1990s demonstrated the wood products industry’s commitment to meeting the increasingly stringent air pollution control regulations imposed by the Clean Air Act amendments. These technological advancements paved the way for further improvements in emission control and set the stage for the industry’s continued pursuit of cleaner air.

Tightening Emission Standards Drive Technological Milestones for Air Pollution Control

As regulations tightened, the wood products industry faced increasingly stringent emission standards for particulate matter, volatile organic compounds (VOCs), and hazardous air pollutants (HAPs). This drove continuous innovation in air pollution control systems to meet the evolving targets. While typical particulate emissions hovered around 0.1 grains/scfd in the 1980s, the industry rapidly progressed through the following milestones:

  • Mid 1980s: 0.05 grains/scfd particulate target.
  • 1990: 0.02 grains/scfd.
  • Mid 1990s: 0.005 grains/scfd achieved with VOC and HAP efficiency requirements reaching 90% and higher.

By present day, standards demand particulate emissions below 0.005 grains/scfd and VOC and HAP efficiencies of 99% and 90% respectively. To meet these rigorous benchmarks, advanced systems like optimized wet electrostatic precipitators (ESPs), even-chamber regenerative thermal oxidizers (RTOs), and rotary valve RTOs tailored for wood dryers were developed – ushering in a new generation of high-performance air pollution control systems.

The Future Beckons – Emerging Trends & Challenges for Air Pollution Control

1. The Demand For Cleaner Air Continues. The public’s appetite for cleaner air remains insatiable, fueled by growing awareness of the detrimental effects of air pollution on human health and the environment. Consequently, industries like the wood products sector must brace for even stricter emission limits, necessitating the development of more advanced and efficient air pollution control systems. To meet this demand, strategies may include:

a. Improving Existing Control Systems – Wet electrostatic precipitators (ESPs) have been enhanced to achieve lower particulate emissions, with recent data showing emissions approaching ambient air levels.

b. Implementing Catalytic Oxidizers – Converting regenerative thermal oxidizers (RTOs) to regenerative catalytic oxidizers (RCOs) can enhance VOC and HAP control while reducing greenhouse gas emissions, as RCOs operate at lower temperatures and offer improved energy efficiency.

c. Explore New Tech. The industry is investigating advanced filtration systems and innovative scrubbing techniques to address emerging pollutants of concern and meet the ever-tightening emissions limits.

2. Reducing Greenhouse Gas Emissions. The wood products industry recognizes the need to reduce greenhouse gas emissions from its operations, and are exploring the following strategies:

a. Converting RTOs to RCOs. Regenerative catalytic oxidizers have lower operating temperatures (around 800°F for RCOs compared to 1550°F for RTOs), resulting in reduced fuel consumption and associated emissions. They also have improved energy efficiency, with a cost savings example showing annual fuel cost savings of $617,400 to $1,356,500 for an RCO system compared to an RTO system, depending on fuel costs. Finally, the smaller combustion chamber, reduced fan horsepower requirements, and lower system pressure drop of RCOs, further contributes to energy savings and emission reductions.

b. Implementing On-Site Green Power Generation. This includes site-specific solar collectors that provide a renewable energy source for industrial operations, as well as, using untapped run-of-river hydro resources, as a potential source of green power generation for smaller industrial use.

c. Utilizing Catalytic Oxidizers. Catalytic oxidizers, such as RCOs, are widely used in the wood products industry for various applications, including veneer dryers, pellet coolers, and medium-density fiberboard (MDF) presses. These systems effectively oxidize organic particulate matter and volatile organic compounds (VOCs), reducing the need for supplemental fuel and associated greenhouse gas emissions.

3. Improving Technical Expertise and Safety Practices. The wood products industry needs to enhance its technical expertise in air pollution control by employing well-trained engineers who specialize in designing and operating advanced air pollution control systems that incorporate best available control technology.

Additionally, emphasizing workplace safety through proper equipment design that follows industrial safety standards is crucial. This includes incorporating design features like adequate access for maintenance, proper labeling of hazardous equipment, and ensuring compliance with applicable regulations like equipment certification requirements from recognized safety organizations.

Partnering For A Sustainable Future With LDX Solutions

As a pioneering provider of air pollution control solutions, LDX has been at the forefront of the wood product industry’s transformative journey towards cleaner air. With decades of experience and a comprehensive portfolio including wet electrostatic precipitators (ESPs), regenerative thermal oxidizers (RTOs), and regenerative catalytic oxidizers (RCOs), LDX Solutions offers tailored air pollution control systems to address the industry’s unique challenges. Leveraging cutting-edge innovations and extensive expertise, they partner with clients to implement state-of-the-art technologies, and achieve environmental objectives while ensuring operational efficiency and regulatory compliance.

If you seek to enhance your air pollution control strategies, explore catalytic oxidation for your wood dryer operations, or require guidance on meeting future emission standards, LDX Solutions invites you to engage with their team of seasoned professionals. Visit to learn more and unlock the potential for a greener, healthier future.