Multi-Staged Combustion or Selective Catalytic Reduction?

Comments Off

The Challenge

Many industrial furnaces operate in oxygen depleted conditions, emitting high levels of ammonia, NOx, and other nitrogen-bearing compounds. This presents a significant challenge for manufacturers striving to meet air quality regulations and limit carbon output.

Emission streams that contain nitrogen bearing hazardous air pollutants (HAPs) cannot be thermally treated in a traditional oxidizer system without forming additional NOx, making adherence to an air permit difficult or impossible. In such cases, a secondary abatement device, downstream of the thermal oxidizer is required for additional NOx reduction.

Historically, the industry has relied on Selective Catalytic Reduction (SCR) systems to achieve this. The add-on technology injects ammonia or urea into the process stream before passing it through a specialized catalyst that converts the NOx into nitrogen gas (N2) and water vapor. However, this approach comes with significant operational burdens:

The need for ammonia or urea storage, pumps, and customized control systems to maintain injection rates.
High operating costs due to chemical consumption, catalyst maintenance, and periodic replacement.
Fresh air must be added to dilute the inert process streams to safe levels, increasing the treatment volume and leading to condensation issues.
Additional winterization equipment to prevent freezing in cold water climates.

It essentially requires a small chemical operation to remove the NOx and the staff to support it.

The Solution

Over the past four decades, Anguil has provided thousands of thermal and catalytic oxidizers around the world, many of which incorporated SCR technology. Recognizing the inefficiencies, engineers at Anguil came up with a better solution. The objective was to maintain very high levels of HAP removal, eliminate the catalyst and associated maintenance, prevent the need to dilute the stream making it safer to operate, and eliminate the use of add-in chemicals.

This solution was a Multi-Staged Direct Fired Thermal Oxidizer (MS-DFTO) – a groundbreaking approach that compartmentalizes the oxidation process across multiple temperature-controlled stages with varying oxygen levels, to dramatically reduce the formation of greenhouse gases.

In the MS-DFTO the nitrogen bearing HAPs are introduced into the first stage of the thermal oxidizer, the reducing zone, that operates at elevated temperatures, but without oxygen. This serves to disassociate the HAPs while not forming NOx from any nitrogen bearing compounds in the absence of oxygen. Special operational sequences ensure starved oxygen is maintained in the first stage. The high temperature, oxygen depleted gas leaving this first stage is then rapidly cooled in a second stage to near the oxidation temperature. At this cooler temperature, the gases are reintroduced to air in the third chamber where the complete combustion of compounds occurs. Design considerations are made to ensure that the temperature after oxidation does not escalate to where thermal NOx could be formed, generally above 1,800°F (982°C).

Specialized refractory insulation and highly automated controls for the various stages of the Anguil MS-DFTO minimize auxiliary natural gas consumption. Properly staging the operating conditions and temperature profile throughout the MS-DFTO will result in destruction rates of the hazardous compounds and volatile organic compounds with minimal NOx formation in a single system.

In select applications, a fourth stage of the MS-DFTO has been added to provide Selective Non-Catalytic Reduction (SNCR) as a safety factor to ensure even fewer NOx emissions. Experience has shown that these fourth SNCR stages are not necessary and rarely used even when supplied as the NOx emissions have always met permit requirements without the need for this polisher.

The Result

This staged combustor from Anguil is reshaping how industries approach greenhouse gas abatement from process furnaces. On this application, the Anguil MS-DFTO was treating 5,000 SCFM (8,025 Nm3/hr) of process air in a single abatement device with well over 99% HAP destruction and NOX emissions that were a small fraction of the allowable permit value. The equipment does not require chemical injections or active catalyst maintenance, meaning a heavily reduced operational cost relative to an SCR. Inert process streams can remain inert, meaning a safer system can be supplied that does not require upstream dilution. Treating a fraction of the air also means the upstream process ducting can be smaller, saving cost all around.

Industrial facilities continue implementing Environmental, Social, and Governance (ESG) strategies to comply with regulations, improve sustainability, and meet stakeholder expectations. This ESG initiative met those objectives and reduced equipment cost, footprint, and maintenance costs, while eliminating the carbon footprint from past chemical purchases.

Onsite Wastewater Treatment for an On Point Budget

Comments Off

The Challenge

A global manufacturer of key chemical ingredients used in a wide array of products including clothing, carpeting, automobile thermoplastics, computer cases, and sporting equipment, was planning a facility relocation and expansion that presented a significant wastewater treatment challenge.

At their previous location, the manufacturer was using a perozone system to treat their cyanide-laden wastewater. However, the system as designed could not meet the rigorous discharge standards of the local Publicly Operated Treatment Works (POTW) on the order of 0.04 ppm. Further, they had abandoned the peroxide injection system to reduce the health and safety risks per a companywide mandate.

The expansion required a relocation to a new facility, but the increased production would also triple the company’s wastewater volume. If they did not find an onsite treatment solution, the hauling and disposal costs were going to dramatically increase operating expenses.

The Solution

Nailing Down the Requirements

Anguil collaborated with the client to understand their specific challenges and determine the project objectives. We gathered benchmark data at the existing facility to identify possible solutions that offer the best return on investment (ROI). Project engineers then worked with the customer to understand their decision-making criteria to evaluate only business viable treatment approaches.

In this case, the client’s priority was to eliminate hauling and disposal costs of their cyanide-laden wastewater. With the expansion at a new facility, they expected their wastewater volume to triple, as well as the corresponding disposal costs. Secondly, they wanted a fully automated system with minimal operator intervention so they could focus on producing products. Third, they wanted to minimize the storage and handling of any noxious chemicals.

Next, water samples were sent to the Anguil lab to validate the different technology considerations. Anguil typically identifies several potential treatment and process options which align with the client objectives, and after presenting these to the customer, collaboratively selects one or several to validate. Anguil proposed several oxidation schemes. The client preferred to move away from ozone and peroxide so alkaline chlorination was selected for this project. It is a well-known method with wide application to similar waste streams and is easily automated.

To validate the treatment process, the customer elected for both a bench trial as well as a scaled pilot. For the bench work, the client provided 5 gallons of wastewater collected from their existing facility. Using the required caustic and bleach treatment protocol and measuring free HCN content via the USEPA Pyridine Barbituric Acid Method (Method 10265), test samples were returned which were below the POTW limit of 0.04 ppm. Based on the bench tests results, chemical dosing requirements and costs were easily established before the system was even installed.

Bench Verification

Figure 1 – As received waters from the two (2) drums of HCN wastewater marked 1 and 2 respectively. (Right) HCN wastewater post treatment.
Figure 2 – Example HCN measurements. Non-detect is shown on the right, over range on the left.

After the validation that the method would work, albeit on small sample volumes, the customer requested that Anguil perform a larger pilot study to both validate that larger batch treatments would perform similarly. For the pilot work, the client sent Anguil two (2) fifty-five-gallon drums of wastewater. Adapting an existing pilot system, the same reactions were performed at the previously determined set-points on 15- and 25-gallon batches. Again, final concentrations of HCN were below the required discharge limit. In addition to the further treatment efficacy validation, the chemical dosing requirements were used to estimate yearly operational expenses for the full-scale treatment system as well as size and design the required chemical reagent storage capacity.

Figure 3 – Appx 15 gallons of HCN wastewater before treatment (left) and after treatment (right). Again, the cloudiness is due to the formation of the precipitate.

Putting it all Together

The final step in the process is the system design, realization, and installation. Anguil put together the proposal for a fully automated batch treatment system to handle their expected treatment volumes. The proposal contained specifics on many mechanical components including the tank, pumps and mixer sized as well as the advanced automation and controls – including integration with their existing infrastructure and DCS system – to meet their requirements. Additionally, the appropriate service options for installation, installation supervision, commissioning, and training were included. After the system was installed, Anguil performed a 3-day start-up and training including verification of the system’s ability to treat the wastewater. Anguil’s Aftermarket team will be there to service and support the client as needed.

The Result

Anguil’s approach to solving a client’s wastewater problem is to take a wholistic view of the challenge with a series of go/no go steps throughout the process. Project Engineers are always focused on the customer’s business objectives in a collaborative effort to define an efficient and cost-effective trial to validate treatment approaches that align with their objectives. Through the bench and pilot testing, we offer insight gained along with a comparison of pros/cons of the treatment approaches until we get to the treatment system that aligns with the client needs.

As a system integrator with 35+ engineers and 60+ supporting personnel, we take a technology agnostic approach to help our clients get the system they want. In this case, the results from our effort:

Client walked through a collaborate process to ensure key decision criteria and objectives were met in a timely and cost-effective manner.
Customer was able to evaluate various oxidation treatment options that aligned with safety and cost parameters.
Lab and pilot validation trials confirmed treatment approach and provided operational expense estimates to client as requested.
Anguil provided a single-source system integration approach that included all engineering (Mechanical, Electrical, CAD, Project Engineering) and support services in-house to mitigate exposure to risk and deliver a fully integrated system with install, commissioning, and training support.
The treatment approach saved the client considerable amount of money versus hauling and disposal services; providing an ROI estimated in the 14-16 month range.
Anguil’s electrical engineering team developed the automation and controls to automate the batch-treatment process. This results in minimal human interaction and an extremely efficient process. It also proactively notifies them via text and email of system condition, need for chemical reorder, reporting and remote login capabilities.

Note: At the time of bench and pilot testing this wastewater, Anguil was engaged with a second wastewater produced by the client. We followed a similar approach and validated treatment efficacy through lab and pilot studies. The result of onsite treatment for both wastewaters offered the client an incredible cost savings with minimal impact to resources.