In a world where environmental concerns take centre stage, it’s crucial for industries to embrace sustainable practices and reduce their emissions. One pressing environmental issue is the presence of nitrogen oxides (NOx) gases, which have a detrimental impact on air quality and human health. To tackle this challenge head-on, Pressure Worx, in collaboration with AECOM, has recently designed and supplied a new NOx scrubbing solution to Koppers in Wiri, Auckland as part of a site upgrade.

NOx gases comprise highly reactive compounds, mainly nitrogen dioxide (NO2) and nitric oxide (NO). They are byproducts of various industrial processes, in this case, stemming from an arsenic acid reactor used in the production of wood treatment chemicals. These gases contribute to air pollution, leading to smog formation, acid rain and pose a significant threat to respiratory health.

In 2021, Koppers initiated a project to upgrade their Wiri production facility. Pressure Worx had previously provided a heat exchanger for their existing plant and collaborated with Koppers and their engineering consultants at AECOM to design a larger uprated heat exchanger for the project. The project also required a new updated NOx scrubbing system. Leveraging Pressure Worx’s extensive experience in biogas scrubbing worldwide, we were initially contracted to support and review the Koppers/AECOM process, providing mechanical design services for the system. This collaboration ultimately led to the award for the manufacture and supply of five large stainless steel scrubber vessels, in addition to the uprated heat exchanger, in late 2022.

In the emission reduction process, NOx gases generated from the arsenic reactor enter Pressure Worx’s 3-meter-long stainless-steel shell & tube heat exchanger cooling the gas before it enters the multistage scrubbing tower solution. This consists of five scrubbing towers, each with a 1.2-meter diameter and heights of approximately 11 meters, connected in series. Inside the scrubbers, a series of chemical reactions occur, neutralizing and removing the harmful NOx gases from the exhaust stream.x

Pressure Worx provided the scrubbing towers, complete with stainless steel internals (liquid and gas distributors, packing supports, and hold downs), ceramic random packings, quick-release inspection/service manways, and handholes. Additionally, Pressure Worx designed and supplied the level transmitter chambers and manufactured the in-ground foundation steelwork and stud bolting to ensure a seamless installation on-site.

Pressure Worx successfully delivered all the equipment to Koppers’ Wiri site on schedule in August 2023. They now proudly stand as part of Koppers’ newly upgraded Wiri process facility, another milestone in New Zealand’s environmental efforts.

NOx scrubbing system