Environmental Challenges With Component Cleaning
A story from Tony's career ...
POSTED BY ELLEN WILLOUGHBY ON 02/07/2020 @ 8:00AM
More from my colleague Tony, this time talking about environmental challenges around component cleaning, with an example from his career of the dangers of using pressurised oxygen. Over to you Tony ...
Do you have any chemical processes that you think should be looked at to see if you can reduce impact on the environment?
copyright: mulderphoto / 123rf
Some years back I was associated with a company that made equipment for use with high-pressure oxygen. At that time, I didn't fully understand the dangers associated with oxygen. At atmospheric pressure, oxygen feeds a fire.
If it is present in higher concentrations, materials that might not usually burn can be more easily ignited, the fire will burn hotter and more fiercely and it may be impossible to put it out. But pressurised oxygen is susceptible to autoignition- no spark or flame needed, just an energy source and something to oxidise.
"One such process for autoignition is adiabatic heating of the pressurised oxygen!"
This occurs, for example, when a valve is suddenly shut in the pressure line. If this pressurised oxygen were to come into contact with hydrocarbon contamination in the line, the heat produced could be sufficient to react with the contamination to cause an ignition, potentially resulting in rupturing of pipework or associated equipment and thus a major safety incident in that and whatever might follow.
I give you this information as a backdrop to the processes necessary to establish cleanliness of product for use with high-pressure oxygen. The company I was with had well-established customer approved cleaning processes and it certified products as 'cleaned for oxygen service'.
Equipment was manufactured from silver soldered cupronickel alloy and high tensile brass components (materials of construction are also important, since melting point and potential for oxidisation are important factors).
The initial cleaning process utilised chromic acid to remove flux and other deposits. However, although components would come out of the final cold water rinse looking like jewellery on the exterior, the internal passages would not be sufficiently clean and thus had to be flushed with solvent, in this case, trichloroethylene ('trike'), followed by a nitrogen purge. A complex and unpleasant process, but totally necessary to avoid any risk of the disaster scenario outlined above.
As the years progressed, life with these processes became more difficult for me as Operations Manager, both from an environmental and an occupational health and safety point of view. Already burdened with the cost of consent to discharge waste rinse water, astronomical water bills for copious water usage, and high waste acid disposal costs, there was also the Solvent Emissions Directive (SED) to consider.
As a user of trike, and not having a hermetically sealed process plant, a permit was needed from the council since our usage exceeded the 1-tonne annual threshold set in the Directive. And what were we doing about our reduction scheme, also a requirement?
Since the company was by now certified to ISO 14001, pressure was growing on me to look at more environmentally friendly processes. Then came the final blow in 2006 - The Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), designed to address the production and use of chemical substances and their potential impact on health and the environment.
With chromic acid and trichloroethylene both being carcinogens, these were on the hit list of 'candidate substances' to be abolished (unless you wanted to plead a special case for use ... seriously, don't go there!).
"There followed a period of researching alternatives!"
In terms of dipping, essential to effectively remove flux residue, the choice was between nitric acid - even worse than the current process, with major safety concerns - and hydrogen peroxide. Hydrogen peroxide looked like a panacea, and it appeared that it would do the job, didn't present the same dangers to health and was environmentally easier to deal with.
In tandem with this, I was looking at flushing and had discussions with various manufacturers of aqueous washers, the preferred environmental solution, but none were prepared to commit to achieving the levels of cleanliness required. I, therefore, looked at alternative solvents.
The easy answer would have been to change to perchloroethylene, better known as 'perk', and widely used by the dry cleaning industry. My view though was that since perk was also a chlorinated solvent, it was likely to be on the list for banning some way down the line, and was still bad for the environment.
Our bigger issue was the need to invest in a new cleaning plant to handle the solvent; the existing flushing plant was a leaky cauldron and converting it to perk wouldn't get us over the SED problem of excessive solvent usage and potential associated health risks.
By this time, fluorinated solvents were becoming more readily available and whilst the cost differential between fluorinated and chlorinated was 10:1, as trike supply started to dry up the cost differential narrowed. These fluorinated solvents were effective cleaners, not carcinogenic, safer to use and deemed environmentally friendly as they don't destroy the ozone layer.
We duly set about trialling the hydrogen peroxide dipping and solvent flushing processes and preparing samples to submit for cleanliness testing, and after much discussion with the customer about why these changes were necessary, both processes were eventually approved.
After much deliberation, we took the plunge and invested in a fluorinated solvent cleaning plant which, whilst not hermetically sealed, was designed to minimise solvent loss.
Now, as is nearly always the case, taking a process from a trial to production is never straightforward. With the hydrogen peroxide, new acid vats were duly made and installed and the process introduced. What quickly became apparent was the highly unstable nature of hydrogen peroxide, and its readiness to decompose, self-heat and boil off.
One night I was working late when a member of production rushed into my office to say he had a problem. When I got to the acid shop, the hydrogen peroxide vat was boiling furiously with a thick cloud of vapour above it. It's probably on YouTube somewhere.
Not being a chemist, and finding the experience un-nerving, I was wondering if it was it going to ignite. I remembered reading that Hitler had used it in rocket motors!
"I contacted the National Chemical Emergency helpline!"
They advised that hydrogen peroxide was susceptible to decomposition and would boil away, which it did so, but not before damaging the vat. I then spent a lot of time and effort with the manufacturer of the dip on establishing the cause, since they had not previously encountered the problem. It was concluded that there was a build-up of contamination from hydrocarbons and metal particles from the process as it etched the surface of the product. Much work was put into preventing decomposition through filtration and additives, but not before several more vats of solution were lost.
The introduction of the fluorinated solvent process was less dramatic, except that it was around the time that everybody was trying to stop using trike and we waited 8 months to take delivery.
The last area I looked at was water consumption in the cold water rinse. In the early days, when acid dipping was in process, the operator would turn the cold tap on in the morning and leave it running for the duration; a weir system drain just kept the vat full of cold water. I would wince whenever I saw this tap running; the rinse process was accounting for around 1,150 cubic meters of water usage per year!
I researched how we might better control this process and found a system that monitored water pH and conductivity and worked in conjunction with a solenoid valve on the water supply. If the monitoring fell outside a certain range, the water valve would open. This worked well and greatly reduced water usage, giving an immediate environmental benefit.
"What did I learn from this experience?"
That it can be painful moving away from established processes, and that in neither case was the substitute as effective as the original. But it can be done. And had to be done. I'm pleased to have been the driving force behind it.
Until next time ...
Would you like to know more?
A huge thank you to my colleague Tony Foster for this week's blog post!
If you have any chemical processes that you think should be looked at to see if you can reduce impact on the environment, why not talk to us? Why not call us on 01858 414226, leave a comment below or click here to ping over an email and let's see how we can help.
About Ellen Willoughby ...
I'm Ellen, Director of All About Quality and All About Productivity. I have over 20 years experience as professional in the quality world and 17 years as a practising Buddhist. As a result of this, I have a passion for improvement. in both business and personal life.
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