Heating equipment specialist Hurll Nu-Way recently supplied gas trains and control panels for a complex soil remediation project at an RAAF base in Victoria.
Contamination control and mediation experts Enviropacific recently built a mobile soil remediation plant at Point Cook, for which Hurll Nu-Way supplied two 50Gj/hr gas trains and control panels for burners, and subsequently installed and commissioned them.
Clean-up of RAAF Base area
EnviroPacific are experts in handling contamination problems throughout Australia, performing remediation, water and vapour treatment, thermal treatment and other services. They can handle a variety of contaminants, such as hydrocarbons (diesel, oils, gasoline) and have technical expertise in assessing, handling and processing liquid and solid waste from contaminated sites.
Back in 2012 they were appointed as a remediation contractor for the clean-up of the former fire training area at the Williams RAAF Base in Point Cook, which was one of the most complex remediation projects in Victoria. Due to fire-fighting and other activities, the underlying soil and groundwater of the area were contaminated with organic hydrocarbons, requiring preventing potential risks to the environment and to human health.
Among the technologies used for soil remediation, treatment by thermal desorption technology is becoming more common. It is a quick and reliable method to remove or destroy contaminants on site. EnviroPacific applied direct fired thermal desorption technology, installing and commissioning the Direct Thermal Desorption (DTD) plant, with the soil processing line from the USA.
The line included a desorber to dry the soil and drive off organic contaminants, and an oxidiser to render the contaminants harmless and suitable for discharge to the atmosphere.
The desorber and oxidiser were each supplied complete with a burner, each burner capable of an output exceeding 50Gj/h.
In order to ensure compliance with Australian Codes and to meet Energy Safe Victoria approval, the fuel trains and the burner management panels were sourced in Australia.
Installation of gas trains
Hurll Nu-Way, known for their involvement in several large energy saving projects and their expertise in burner controls, was awarded the contract to design, manufacture and supply the gas trains and the local burner panels for each of the burners.
They also installed the gas trains and were responsible for liaising with Energy Safe Victoria over the system approval and carrying out the burner commissioning and start-ups.
The plant is constructed allowing for the possible relocation in the future: the gas trains and panels were designed to allow their transport by road to new sites; while the burners, currently running on LNG, can operate with natural gas, LPG or oil.
Difficulties with plant construction
One of the difficulties in the construction of the plant was its location – near the coast of Port Philip Bay airfield – opened to harsh weather conditions (heavy winds and presence of salt in the air), and under an active airfield. These conditions put limitations on the construction of the plant's components, including the gas trains, which had to be rugged, reliable and repeatable.
Gas trains' features
To meet these demands, Hurll Nu-Way supplied equipment with the following features:
- Filters and pressure regulating equipment with over pressure shut-offs (OPSO). Independent pilot gas rate regulators with OPSOs were installed in the pilot lines to ensure reliable pilot ignition on start up.
- Pneumatically-operated double-block safety shut-off valves were included in each gas train with a valve proving system to check their effectiveness prior to each start up and after each shutdown.
- Self-checking ultraviolet flame detectors are fitted to each burner to operate in conjunction with the panel mounted Siemens LGK ignition and flame detection programmers in a system designed to operate 24 hours per day, 6 days per week.
- Control of the firing rate of each burner is performed through motorised linked valves – a butterfly valve in the air line and a square port valve in the gas line assembled in tandem and positioned by a Honeywell motor.
- The linked valves option controls the burners at a fixed air/gas ratio and so are less flexible than alternative schemes using independent actuators but they offer reliable and repeatable control which is very important with this application.
The burner systems are monitored and controlled by the plant's PLC control system, but the burners' ignition and safety system is hardwired as required by current Australian codes.
EnviroPacific incorporated safety features into the system beyond that required by a strict interpretation of the Australian Code.
Hurll Nu-Way assisted in interlocking two burners by the overall control system. Although the burner systems are independent of each other, the overall control ensures that the oxidiser burner is started first and its chamber reaches a pre-set minimum operating temperature before the desorber burner system can be started.
Products of combustion together with water vapour and volatiles from the soil are drawn from the desorber and through the oxidiser. The temperature in the oxidiser chamber is maintained between a minimum of 7500C and a maximum of 11000C with excess oxygen present in the process stream to ensure the total destruction of the contaminants.
The pressure inside the processing line is maintained below the atmospheric pressure to prevent any leakage of the process stream to the atmosphere.
Exhaust gasses being delivered to the stack are continuously monitored for oxygen, carbon monoxide, NOx and SOx to ensure complete destruction is achieved.
Additionally, NATA-registered testing was regularly carried out to analyse the gases for a comprehensive suite of parameters including VOCs, SVOCs including Dioxins and Difurans, metals, acid gases, and particulate matter.
Currently, the plant is operating remediating 20-25 tonnes of soil per hour, with circa 60 000 metric tonnes of contaminated soils and 18 ML of contaminated groundwater successfully treated and reused on site.
Hurll Nu-Way is proud to partner with EnviroPacific to provide a very complex solution for soil and water remediation.