What are the safety requirements for a Steam Boiler Blowdown System?
The HSE previously gave guidance on the blowing down of steam boiler systems under Health and Safety Guidance Note PM60 Steam Boiler Blowdown Systems 2nd Edition 1998, this has now been withdrawn, and replaced with Guidance for Industrial Steam Boilers (BG03).
Guidance for Industrial Steam Boilers (BG03) is a guidance document intended to provide advice to designers, specifiers, manufactures, installer and those responsible for the management and operation of steam plant as well as the Competent Persons. The latest document (BG03) is applicable to both new and existing installation of steam boilers.
How can Valveforce help you?
Valveforce can offer you the peace of mind that you are working in Compliance with the HSE guideline BGO3 and ensure that your bottom blowdown is handled in the correct manner. Our team of experts can be relied upon to offer advice and subsequently carry out complete boiler house and boiler surveys.
In the boiler house we will:
- Investigate feed-water conditioning
- Supply boiler feed-tank and deaerator plant
- Provide water treatment equipment such as softening and RO plant.
With the boiler we:
- Review boiler control equipment for level control
- Check boiler blowdown
- Test boiler heat recovery equipment
Valveforce will produce a detailed reports to ensure that our customer’s boiler houses are up to date with the latest standards and legislation. Should you want to see if you are complying or require further advice, please contact Valveforce on 0121 7111 908 and ask for the boiler house specialist team.
What is Steam Boiler TDS (Total Dissolves Solids?)
To get to the bottom of the topic we’ve let our in house specialist explain: Imagine you have a saucepan of boiling water and let all the water evaporate, there will be some left over deposits left on the bottom of the pan. This is all the impurities left behind as the “clean steam” has evaporated off. Now imagine this on a large industrial scales, it becomes a serious problem that need to be measured, monitored and managed.
With an industrial steam boiler, as the water in the boiler evaporates off into steam it leaves the impurities behind, thus making the boiler water more and more concentrated with TDS. If this is not managed it could consequently coat the inside of the boiler and the fire tubes making them in efficient and dangerous, or foam, prime and carryover.
The more these deposits build up, the more inefficient the boiler can become:
- High TDS – Could lead to Plant & Production downtime, situations like cold spotting on process heating /cooling batches, often costing thousands in waste and poor product quality. If the boiler is priming (foaming) then you can be certain that all the pipework, valves and steam traps will be getting a coating of deposits on them. The knock on effect of this is often poor heat transfer, steam traps failing open or sticking locked and valves seizing up with deposits
- Low TDS – On the other hand by having a too low total dissolved solids reading, can lead to blowing down too much heat energy contained within the heated and chemically treated water, leading to noticeable increases in costs of fuel & chemical treatment
It is therefore essential to ensure accurate blowdown methods in order to maintain steam quality. The team at Valveforce is relied upon to offer advice, carry out boiler blowdown survey, and conduct detailed reports to ensure that our customer’s boilers are being blowdown safely, efficiently and in accordance with BG03.
A Valveforce focus on Boiler Blowdown
When it comes to steam boiler blowdown everyone must be conforming to Blowdown Systems, Guidance for Industrial Steam Boiler (BG03). If you are unsure or need clarification then advice should be sought to get the specialist knowledge that may be required.
There are three main type of steam boiler blowdown:
1) Bottom blowdown:
This is required to discharge the deposited solids and sludge that drop to the bottom of the boiler shell which need regular clearing via the rapid action of a bottom blow down valve.
This bottom blowdown valve is either manually or pneumatically actuated to ensure a quick dump of high pressure boiler water to jolt up the bottom of the boiler and suck out any debris / particles that have deposited there.
In general the valves should be blasted for three to five seconds once per shift, any longer for the bottom blowdown, then that will be wasting valuable heated and treated hot boiler water. The bottom blowdown water can be discharged into a suitable blowdown pit or more commonly a specific boiler blowdown vessel.
The advantages of a blowdown vessel over a blowdown pit are:
- They are fraction of the cost and size, of a blowdown pit
- Quick and easy to install
- Low maintenance solution for the replacement of blowdown pits
- Safe- no cover plate to lift or open area for staff to fall into
- Dissipates heat more readily
The blowdown vessel can also designed to safely handle continuous blowdown, blowdown from level control chambers and level gauge glasses. It can also accommodate other high pressure drains providing it has been sized to do so.
2) Boiler Continuous blowdown
Here we are looking at the management of the Total Dissolved Solids (TDS) or the solids in suspension contained within the water inside the boiler.
To monitor this it is very common to have a stabbing on the side of the steam boiler shell feeding a conductivity probe into the water itself to send a conductivity signal back to the TDS controller. The TDS controller will then measure the TDS reading and open / close the TDS control valve in line with the set point and the proportional band (+/-) the water TDS level is to control at.
Typical TDS Control System
Valveforce can design and supply you with the ancillary equipment associated with boiler blowdown: TDS Controllers, Conductivity Electrode, Control valves, Globe Valves, Check valves and Automatic Blowdown Valves. The blown down TDS water is valuable as it has been heated, so in order to recover this heat it is very common to recover the energy via a continuous blowdown flash vessel system.
At Valveforce we aim to recover as much energy into the boiler feed-tank, by pre heating the feed water and using the flash steam to direct heat into the feed tank. Find out more about Flash Vessels here.
3) Boiler Sight glasses:
At Valveforce we understand the importance of proper cleaning and maintenance of the water column and the water gauge glass, or sight glass.
The water gauge glass on a boiler enables the operative to visually observe and verify the actual water level in the steam boiler. However, if not properly cleaned and maintained scale can build up and a gauge glass can seem to show that there is sufficient water, when the boiler is actually operating in a low or low water condition. The water column must be kept clean to ensure the water level in the gauge glass accurately represents the water level in the boiler.
All plant operators must undertake proper blowdown procedures in order to keep the water piping clean, even if the probes remain clean for extended operational periods. The risk for sediment build-up in the water piping is quite high and the user may consider their local water quality as an influencing factor to determine the frequency of the blowdown.
After performing the blow-down procedure, if the water level does not return to normal promptly, the connecting piping may be partially clogged and have to be cleaned.
The sight glass blowdown water is often return to the Boiler blowdown vessel, in a separate line.
Valveforce blowdown vessels are designed to cool down water from boiler purges including:
- Bottom blowdown
- Level gauge glass blowdown
- Level probe standpipes blowdown
- TDS continuous blowdown
The above information is a quick overview and for information only. Our in house boiler specialist can offer technical advice, carry out boiler blowdown surveys and conduct detailed reports to ensure that your boilers are being blowdown safety, efficiently and in accordance with BG03.