Help sought for temperature control of coal boiler.

Status
Not open for further replies.
N

nixy

New Member
Hi All

My first post & hoping some might be able to help. I’m sure you guys have been asked the same thing many times before, but hopefully some help will be forthcoming.

The Problem.

I have an old Coal fired central heating boiler. The temperature is controlled by a bulb & capillary thermostat sensor mounted on the side of boiler. that starts a fan when the temperature is low. However, due to the mass of the boiler (and water) there can be a temperature lag between the boiler and the coals. So, when the water pump is off, the boiler & water temperature can remain higher than the coals. So in certain conditions the coals go out.

In short, I would like to control a fan (240v ac 0.2A) dependent on a temperature between roughly 20C - 100C and would to be able to adjust the upper & lower temperatures.

I would really like to, not only try and, with your help, build this, but also, understand the build / circuitry.

There are other aspects that I would like to have a look at, but probably best just stick to a less complicated solution for now….. a servo to control an air valve to restrict air flow through the fan in windy conditions.

Cheers

Nick
 
Its all about the sensor. Where will you be measuring the temperature? In liquid? In the combustion chamber?
 
What type of boiler design is it?
A stoker system or a manually fed lump system?
What is its physical size and design?
Approximate weight, water volume, and BTU capacity?
 
The flue is giving a wide range and is more directly related to the coal fire temp. That's where the sensor will be placed.
 
Then you will probably need a sealed temperature sensor sheathed in stainless-steel or a thermocouple. The flue is likely to be a very corrosive environment. Visit Omega to see what type of suitable sensors they have.
 
The sensor I've been using for data logging has been surface mounted, No corrosion worries.
 
Are you asking for a circuit that will switch on/off an AC load based on the temperature plot above?
If so, what voltage does the sensor put out at the desired turn on/turn off temperatures.
 
I dont see how you plan to maintain the water temp by sensing the flue gas temperature. Its like saying I want to control the speed of my car by reading the exhaust temperature. Flue temp is a byproduct of the heating effort and nothing else. Flue gas temp is only a good referance for how efficient your system is.

Water temp is based entirely on available BTU's of the fuel being burned, the thermal mass of the system, and any thermal loads drawing heat out of the water.

I have worked with boiler systems for some time now and have custom built multi fuel source capable boilers that can burn anything from coal, any grade of wood, garbage, or basically anything that is flammable really. All of my boiler designs are now using digital controls I designed myself and are smart enough to maintain themselves with any grade of fuel.

Coal alone is normally a very easy to control fuel for the most part. I suspect your system has problems elsewhere besides the thermostat.
If your snuffing out your coal fire the intake idle draft is set wrong or your coal is of very low grade or wet. Or you are running the system far too cold and its not supporting a proper draft while idle. There are also a number of other factors that can cause your problems as well.
 
Last edited:

Thanks for the reply, but the water temperature has been regulated effectively (manually) by controlling flue temperature.
I take your point regarding draft, which I'm sure is a problem......

...... bottom line?? I want to

control a fan (240v ac 0.2A) dependent on a temperature between roughly 20C - 100C and would to be able to adjust the upper & lower temperatures.
Click to expand...

That's what I'd like to do. It may be beyond my ability. But that is why I posted here...... to get assistance with a temperature controller. I may end up having to get an 'off the shelf' controller & thermocouple, which would be a shame.
 
 
An easy way to make an electronic thermostat is to start with a thermistor, which if used with a simple bridge and opamp circuit can switch a relay or SSR. You suggested that you already have a sensor, but now it seems that we are back to square one! Like I said earlier, everything derives from the sensor, and what voltage (or resistance) it puts out at the temperatures you want it to switch at...
 

I'll take any advice regarding which thermocouple to get.
 
Way to cold for coal or any fuel for that matter.
What your doing is very dangerous and will eventually cause severe property damage or someones severe injury or death.

Limiting the burn times and rates by short cycling the fire is going to create massive stack condensation and coal tar formation. Basically your building your own death machine out of your boiler.

Once coal tar builds up to a thick enough level and gets hot enough it will spontaneously ignite and then it burns hot enough to melt stainless steel chimney liners and shatter chimney brick material. Then the house and everything and everyone in it goes next.

Short cycling a coal fire like that to maintain a low stack temp creates high levels of coal gasification and carbon monoxide as well plus makes for extremal inefficient use of your coal.
Most of your coal never gets burned in the boiler to make heat but is instead uncontrollably gasified into crude but highly explosive natural gas and highly flammable coal tars. Its a bomb and a unstoppable stack fire waiting to happen.

I am not sure where you came up with this idea but its very poorly thought out and will never work as your hoping. Please consult a licensed and certified boiler technician or service engineer and have him rework your system to work as the manufacture intended for it to. Or at least read and understand your manual.

If parts are no longer available and what you have is a home made hack job please get rid of it or get some solid education on how boilers work. If you dont your going to get yourself or someone killed eventually if your house doesn't burn down or blow up before then.

If your doing this to save money please contact your insurance company and tell them what you are doing. They then will happily cancel all of your homeowners and life insurance policies which will have you far more money that way.

Sorry but you really need to know this before going any further with your design.
 

Limiting the burn times and rates by short cycling the fire is going to create massive stack condensation and coal tar formation.
Click to expand...

Yes it would IF it were true. BUT the chimney has NO tar deposits!! What does that tell you?

The system has worked without problems for the best part of 20 years.....I repeat ....with NO tar deposits.

So it would appear you're (your) quite wrong.

But thanks anyway.
 
I think you misinterpreted TCMTech's post.

He said

Limiting the burn times and rates by short cycling the fire is going to create massive stack condensation and coal tar formation.
Click to expand...

Which would mean that just burning wouldn't cause tar formation. It would require short cycling of the fire to produce the tar. So if you had not been short cycling for the fire the past 20 years, then no noticeable tar deposits would have been formed in the past 20 years. Sort of like how burning alone doesn't cause carbon monoxide to be produced. It requires burning in an oxygen defficient environment. Also, you didn't seem to respond to the mention of explosive gasses or carbon monoxide in TCM's response.

I don't know anything about this, I'm just pointing out how your responses seem to indicate misinterpretation of the reply posted.
 
Last edited:
Status
Not open for further replies.

Similar threads

  • Question
LIC Protection - request for help
Replies
12
Views
807
GH Crash
F
  • Question
High voltage startup circuits of flyback controllers (NCP1239 & NCP1219)
Replies
7
Views
979
Flyback
F
E
Resource for designing Electromagnetic Coils - Wire Size, current, number of turns?
Replies
4
Views
2K
EHTDesigner
E
I need some advice on building a battery charger for my bank of 20 Li-ion 5000mAh 26650A
2
Replies
39
Views
3K
rjenkinsgb
V
  • Question
V/F Control Of Single Phase PSC Motors
Replies
7
Views
4K
rguttenb_newb
R
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…