Questioning the ongoing use of chlorine gas – is it the safest method?
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When it comes to purifying water for consumption, there have long been questions raised around the safety of current processes involving chlorine gas. So much so, that the necessity of Emergency Shutdown Devices (ESD) have become as close to an industry standard there can be without formal legislation. These devices, however, are looking like an interim solution for an industry that is now innovating beyond the current practice employed all over the world – chlorine gas could be a thing of the past, and take ESD’s into redundancy with them.
“I think the whole industry will eventually move away from chlorine gas as the conversation around safety and environmental impact becomes more prevalent,” says Matt Wagland, Managing Director of WestWater Enterprises. “While safety is the biggest motivator, cost, transportation, and storage are all playing their part in the search for change too,” he says.
Taking it back to Emergency Shutdown Devices for a moment and in laymen’s terms, ESD’s are installed in chlorine gas plants to reduce the risk of a deadly chlorine gas leak. The automated systems continuously monitor the levels of gas in the air via a leak detector, and should a leak occur, the ESD’s trigger an instant shutdown response and the plant is evacuated of all staff – keeping workers and the surrounding community safe.
While the aim of all ESD’s are the same, they are all not created equal and Wagland describes how the team at WestWater Enterprises are innovating these systems for a sharper and safer response.
“The technique used in a standard shutdown system is a pneumatic, air operated valve but there are some limitations to this technique, basically because it means that you have to store and maintain a whole other energy system in the plant, one that can be faulty,” says Wagland.
“Our team have innovated an electric actuator which works with a specially designed DC motor and gearbox. It mounts on the top of the chlorine gas drum and uses battery power rather than compressed air,” says Wagland. “This device has a lot less chance of fault as it stores its own battery power that holds usage for 24 hours should there be a power outage. The self testing device also checks its own battery every day, limiting staff hours and the risk of a fault.”
“The industry has been employing leak detectors for approximately 15 years, however it is only the last 5 years or so that we have been using the information from the leak detector to trigger an emergency, automated shutdown with the installation of an ESD.”
“ESD’s were historically only installed when the chlorine gas plant was near a school but the Water Corporation are now moving towards a standard where all of their treatment plants will have an emergency shutdown device as well as a leak detector.”
While the need for ESD’s are now high in an industry that employs chlorine gas as the main method for making water safe, the movement towards a whole new disinfectant methodology is becoming imperative. “Chlorine gas is used in most towns in Australia as it is currently the most reliable way to disinfect water, and the easiest, but the effects of chlorine gas to humans and the environment can be dire,” says Wagland. “Our whole job is centered around safety - safety to operators in the workforce, and for houses and communities around the treatment plant - so using an alternative to chlorine gas is a priority for us.”
The Centre for Disease Control and Prevention describe some of the effects of chlorine gas as it removes oxygen from the air and combines with moisture to create an acid, such as struggling to breathe, chest pain, burning pain, fluid in the lungs, and nausea and vomiting.
“In my opinion, no site in Australia will be using Chlorine Gas in the future … It may not ever happen, especially when you are talking about large scale sites such as the Mundaring Weir, but I believe that the Water Corporation will try to eliminate it [chlorine gas] as best as they can.”
WestWater is the sole user of an electrochlorination process in replacement of chlorine gas in Western Australia and have installed the system in mine sites and three community locations for the Water Corporation. “As far as I know, we are the only ones that have completed the whole process and are successfully running electrochlorination plants in Australia,” says Wagland.
Electrochlorination uses a brine solution to create the chlorine in a concealed environment. A large tank of salted water (brine) is passed through a DC cell, therefore removing hydrogen from the solution and leaving the chlorine solution that is then dosed into the water. Creating this chemical reaction onsite means that staff are only buying, transporting, handling, and storing a salt solution which is a lot safer than the highly toxic chlorine gas.
“Another benefit to the electrochlorination treatment process, beyond the safety aspect which is of course the biggest motivator, is that it is a cheaper process,” says Wagland. “Because you are making the disinfectant using salt onsite, there is not the high transport cost that comes along with the movement of chlorine gas.”
Case Study – Donnybrook, WA.
There are sites in Western Australia that are completely ridding themselves of chlorine gas and opting for a safe alternative on offer by WestWater, electrochlorination. RioTinto, for example, have completely removed chlorine gas from their Western Australian miner’s camps, thereby removing the need for ESD’s, as the risk of a chlorine gas leak is non existent now that an electrochlorination process is being used to clean the water.
The Donnybrook site, 200 km south of Perth, has been completely switched over to an electrochlorination plant as of the end of March 2016. This site marks the first Water Corporation site in Western Australia that has completely converted their chlorine gas plant to employ this safer method of purifying water for the staff and surrounding community.
· Location:
Donnybrook is centrally located in the heart of the south west, 200 km south of Perth
· Water supply:
Located approximately 40 km south east of Bunbury on the Preston River, the Donnybrook plant supplies water to the surrounding fruit and vegetable growing industry as well as the rural and timber
industries. The permanent population of Donnybrook is about 3000 and the site is also responsible to provide drinking water to the town. Drinking water for the town is obtained from a wellfield located within the town site comprised of six production bores screened in the Leederville Formation.
· Brief history of the site:
The Donnybrook treatment site is located on the top of the hill in town. Water is stored in a large covered dam and gravity feeds the town of Donnybrook. The site was selected for upgrade due to the age of the chlorination equipment on site and the lack of safety protection such as there being no ESD being used on the site already.
· Population the water supplies:
3000 local people
· Motivation for the move to electrochlorination:
As the treatment plant is located on the top of the hill in town, there is an increased risk to the town should there be a chlorine leak. As chlorine gas is a heavier gas then air, the chlorine would settle down the hill on top of the town.
With this in mind, WestWater and the Water Corporation opted for an electrocchlorination solution. This is the first installation in the state of batching and dosing electrochlorination.
· Plant Specs and costs:
The daily water flow rate of site is 2000m3
Instantaneous flow rate 151m3/hr
The Chlorine dose rate is 1.3mg/l
Chlorine Gas used an hour previously is 200grams per hour
Electrochlorination solution used per hour 24L/hr
Salt needed to make 24L of Electrochlorination solution is 1.2KG
Cost for 1.2KG of salt is 86 cents
Cost for 200 grams of chlorine gas is $1.12
Daily cost of salt is $11.18
Daily cost of chlorine $14.56 + a daily rental cost for the chlorine cylinder $1.24
Yearly cost for salt $4080.70
Yearly cost of chlorine gas is $5314.40 + $452.60 of daily cylinder rental cost.
*Prices above do not even take into account the cost of transporting a dangerous goods (chlorine gas) compared to salt.
**The costs above are based on chlorine quotes from WestWater. The Water Corporation may receive varying prices for both salt and chlorine gas.
· Expected outcomes:
The plant has been running now without fault for 12 months. Operators onsite are extremely happy with the installation and the town of Donnybrook is now chlorine gas free.