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I have a strong background in writing and reviewing technical reports like this. I can tell you with confidence that this is a well written and solid justification for the proposed LFN mitigation measures, and with one possible exception this looks like a very strong technical analysis both theoretical and quantitative in nature, using a robust methodology, extensive technical literature references, as well as in field testing and measurement. Its very good.
Sound reduction achieved is considerable with several further mitigation methods which can be applied if the permit is issued and the analysis has underestimated the noise levels eg amongst other things they can install a sound cancelling systems with the enclosures.
The possible gap which I spotted is that although they have extensive measurements of current LFN at many sites around Hemerdon which might be affected by the TWL operation (which is planned to run 24/7/365), the tests that were performed on site to generate LFN were only done during the day. So, there are no night time measurements from the site. This could be an issue as generally at night air temp is lower, air density higher and sound therefore carries further. The EA if they are being very picky might bite on that. Otherwise its really solid.
If you get a chance to read it I would appreciate your feedback to make sure its as solid as I think it looks. Kind regards.
Good morning croissant, thank you for post. It all sounds very positive. Will this be a issue running the plant at night with sound transmission? I'm not sure if the intention was to run through the night? Can we see this being a problem in your opinion? Thank you in advance.
The plan is that the plant is in continuous operation. If the EA are being difficult they could ask for infield measurement data based on nighttime operational tests from Hemerdon. Doing so would be really messing the project about, but that wouldn't be anything new. After all they sat on this material for 2 months prior to issuing the draft permit and now (as I strongly suspect) have extended the public consultation period (because they internally forgot to circulate for review materially relevant LFN reports.)
Thats 2 months plus another 10 weeks. I'm sure TWL are deeply frustrated. The application went in in 2021. 3 yrs later and they still haven't issued it.
The LFN( low Frequency Noise) report is a very detailed and technical report done by competent people but in 2023 there was no feed in the plant so I presume the screens were run with no mineral feed and the measurements were made with and without plywood ….. so the measurements are only the LFN generated by the machine itself
I am not an expert in LFN
However it is similar to testing the vibration of a washing machine with no clothes in the tumbler !!!!!
Hi Ian - wasn't there some justification made as to why just blocking air flow using the plywood to mask certain proportions of the screens, was a valid test? I'll have a look and see if I can find it. ATB
The question is how much of this back and forth can we take before we go bankrupt?
Agreed. Not too much more. But I think this should be it. If the EA want to close the operation they can just keep delaying and eventually it'll topple under its own weight. Fingers crossed they're minded to issue the permit and looking at the report I think they will.
@Ian - they claim that using the plywood is a conservative model. So why? Although your analogy of the filled washing machine is compelling it contains a few misconceptions. The issue in the far field is noise, not vibration. So to use the washing machine analogy, two streets over you'd hear the washing machine clanking, you would not feel it. What this demonstrates is that it is the vibration at source which creates the noise, and its is the noise which is the nuisance in the far field. Think about a loud speaker. A loud speaker is very loud but it is also very light. So why is it loud? Because of a vibrating surface. Usually a very thin and light vibrating surface. That is likely why they have undertaken the tests using ply. Simply put you don't need the weight, you need a vibrating surface to propagate the sound.
The EA have had very many meetings with TWL. I know, I did a few FOI requests and teased that out of them. I published that data on this board a while back. This has been reviewed extensively by the EA and they are still "minded" to issue the permit.
The reason that this is such a big deal for the EA is that the LFN under WOLF was such a nuisance and gathered so many complaints, the EA classed the LFN at Hemerdon as a "significant pollution". As this is their wheelhouse they are going to make absolutely sure it does not reoccur otherwise they will suffer damning criticism for their incompetence. So because they are minded to issue the permit, this again demonstrates the quality of the report.
21 days to go.
ATB
Hi Ian/Gingy/Croissant,
Just dug back through the history and found these previous reports if you are interested in a compare and contrast exercise.
https://consult.environment-agency.gov.uk/psc/pl7-5bw-tungsten-west-ltd/supporting_documents/NANR45%20Noise%20and%20Vibration%20Impact%20Assessment%20%20EPRAP3203MLA001%20%2031.08.21.pdf
https://consult.environment-agency.gov.uk/psc/pl7-5bw-tungsten-west-ltd/supporting_documents/Noise%20Consultants_2021_1%20Noise%20Compliance%20Report.pdf
Not had a chance to read the latest report yet. I'll try and find a pocket of time.
ATB LB
my understanding from a british manufacture of screens( metso) is that lfn is caused in fine particle separation when there is no escape for compressed air from the top of the screen( co**** fraction ) mesh and the chute that captures the fine fraction …… this is resolved by designing the screens with small portholes in the lateral side to let the air escape
- if there was no feed to the screen then there is no blockage of screen mesh so what is the meaning of the ea measurements
- the new screens purchased from europe are not yet installed in the plant and are stored on the surrounding area of the plant …… so what screens where used in the ea testing ?
can anyone give any more detailed information ?
gives me the impression that top vibration ( secondary harmonics experts ) were employed in this task but were the screen manufacturer left out of these conversations?
spending big capex on boxing in screens is a “ world first * and if proven necessary in the fine screens then it only applies to 2 screens in the proposed circuit
boxing in the “ washing machine “ is the most impractical solution ….. await complaints from the wife and the house maid !!!
They claim its conservative because amongst other things the ply is continuous wheres the particulate feed rate (mass flow rate) will be guaged to prevent sheeting. So the grains are discontinuous and therefore porous to the air , reducing the compression under the unit. The is further reduced by the presence of the diamond shaped holes/perforations which account for 10% of the area of the screen , coupled with a reduced screen size.
The purpose of the exercise is to demonstrate a reduction in the LFN produced. The EA wouldn't commit to specific levels and there's no regulatory acceptable level stated. So TWL have to demonstrate they've taken all reasonable steps to create a reduction, and then on top they've introduced a continuous monitoring system to monitor and detect issues and then proposed additional measures which can be deployed if required to provide further mitigation.
Looks good to me.
What would you want to see done Ian to satisfy yourself that this matter had been addressed properly??
It's an absolute joke! No wonder this country's in the state it's in. They don't see that it's going to create 100's of jobs, they just make it virtually impossible. No wonder all industry and manufacturers go abroad. Too much bureaucracy. Rant over.
there are 14 screens installed in the 1st phase of the twl restart …. most of the screens are co**** screens and the experts ( on screens ) say they do not generate lfn ….. i would like the lfn consultants meet up screen manufacturers to discuss this solution ( boxing in the screen )
twl has experienced mining people ( starting off with neil ) and i am surprised that the twl technical even agree to this solution
is there anywhere in the world that this has been done before ? in my vision , this is a first in the world but i would like some feedback ….. as the saying goes …. never but a “first”
the screen must operate and have maintenance and the solution looks an operational nightmare …. no doubt it may reduce lfn on the fine screening
ian gordon
@ Gingy - relax mate, it'll be fine. But if you feel you must, gird your loins.
@LB - I checked back. These are foundational documents. The later reports are later revisions of these original docs; upgraded info; upgraded methods. Good find though as you can see the back and forth leading to the latest (hopefully last) iteration. ATB.