A few questions from a newbie 1

[dangeroushamster]

Hello folks, I’m an electrician that has recently taken my acs assessment to permit me to work with gas systems. I started out working on catering equipment and then decided that I really wanted to get involved in the industrial heating side of things.

I found a company willing to give me a go and am now happily in my 3rd month with them. However, I am not happy just getting along but really want to get an in-depth knowledge of heating systems and their technologies etc.

So over the next few months you will probably see what you regard as silly questions but just remember I am a newbie

My first question is regarding uv flame detection. I recently went to a job for a burner which incorporated a satronic controller with a uv flame sensor. To cut a long story short the sensor was u/s and I replaced it. But my question is how does this work. It has a + and - terminal. If this is to power the unit then why is there no switch wire or is the + and – misleading and is it just a switch that becomes energized when it comes in contact with the uv rays from the flame. Does it matter which way the + and negative are connected

My second question relates to constant temperature and variable temperature pumps. It seems I get a different answer from each person that I ask so I am non the wiser as to what does what. Anybody shed some light on this one

My third question relates to Efficiency/flue gas analysis. Obviously we want the efficiency to be as high as possible and the co ppm to be as low as possible. I recently came across a forced draft burner that had the blower dampers set to about 50% open. The co ppm was reading at about 90 and I wasn’t very happy with the flame picture. It was more orange than blue. When I opened the damper to about 90% the flame picture was much better and the co was reduced to about 15ppm. Is there a happy medium and how would I know that the flame wasn’t lifting because of my actions (ie opening up the damper and allowing more air). I have seen this on a lot of burners now, and by opening the dampers then the co is reduced and the flame picture is much improved but I figured that the technicians that had serviced before would have changed the damper if it is the right thing to do . If the co ppm is low should I not even be touching this (even if it improves the flame picture). By increasing the air to the burner and thus reducing the co is this improving efficiency. Is it possible to have too much air….will this reduce efficiency/cause lifting/extinguish the flame

Your help on this would be greatly appreciated

/d

 

[pmover]

1) highly recommend contacting mfg of product and obtaining an answer.

2) the question is nebulous; hence, further information is requested. what do you mean by constant/variable temp pumps? i've not heard of such devices.

3) while flame appearance may be used as a guidance by service technicians, it certainly should not be used to determine overall efficiency. i trust the fuel is natural gas? bottom line, any change in combustion air flow will impact overall efficiency and emissions. yes, it is possible to have too much air; thus impacting burner flame and heat transfer capabilities.

-pmover

 

[dangeroushamster]

1. There is no specific manufacturer.... I understand that the rectification electrode alows a very small number of mA to pass through it via the flame. Does the uv sensor work in the same way or does this device simply acts as a switch which closes when a flame is present

2.Constant and variable temp pumps are used on pretty much every heating system that i have come across. AFAIK the variable temps supply the rads etc and the constant temp supply fcu's. Maybe this is a uk thing. Any engineers answer this one I would be grateful

3. I do understand that flame picture should not be used to determine overall efficiency of a burner. This is why we have the flue gas analiser, but is there a rule of thumb for this any help appreciated

Thanks for the input so far

 

[dangeroushamster]

btw yes it is natural gas

 

[imok2]

1. In a gas flame, the infrared radiation will be strongest in the last two-thirds of the flame. The area of the flame that radiates ultraviolet is much more limited than either the visible or infrared areas. Practically all the ultraviolet radiation comes from the first one-third of the flame for all fuels that are premixed with air Consider the UV sensor as a hi impedance resister but when UV light is observed the impedance drops thereby pulling if the flame relay for main flame ignition. It’s important to have + and – in the right order. In the case of ultraviolet detection, an increased amount of light falling on the detector will not necessarily increase the signal. This is because most of the UV is generated in the first one-third of the flame and because of light absorption by the combustion products.

3. A C02 analysis alone does not provide a safe indication of the combustion air/fuel setting. Additional measurements of either smoke or CO are recommended In other words, a given C02 value can occur on either side of the stoichiometric. Excess air is the preferred term to describe the combustion setting on the safe side of the stoichiometric. In order to arrive at the excess air value, an 02 measurement is performed. Combustion efficiency calculations start with assuming complete combustion and then applying three basic factors:
1. The heating valve for a given fuel.
2. Net stack temperatures.
3. Percentage of oxygen by volume.
If we only want to know the efficiency of a particular burner, we need only an instrument to find percent 02, a thermometer, and a combustion efficiency calculator or chart for the fuel being used. Combustion efficiency calculators, such as the Bacharach 10-5064, or combustion efficiency charts, have taken into consideration the heating value of a fuel, so it is only necessary to find the net stack temperature, percent 02, and insert these figures into the chart or calculator.

 

[imok2]

ITEM 2.
a. Varying water flow to finned tube radiation or a heating coil, each supplied with constant temperature hot waterIn both cases, reducing flow 75 percent reduces the heat output only 30 percent because as flow is reduced, more heat is extracted from each gallon of water. At low flows leaving water temperature decreases sharply and at light loads modulating flow control by itself is not the best means of controlling heat output. However, the effects of flow Control on Finned Tube Radiator Heat Output are such that if supply water temperature is also varied (reset) in response to a change in heating load, heat output varies almost linearly. This mode of control appears ideal, except that it is impractical to provide a different hot water temperature to each heating coil or piece of radiation in a building. But varying supply water temperature as a function of outdoor temperature provides a good compromise.

b. Constant water temp supply on FCU is self explanatory because you have constant flow however the hot water temp also can be reset by OSA and the pump turned off .

 

[dangeroushamster]

Thanks for taking the time to reply to my post mate. Very imformative.



/d