effecta lambda boiler temperature data- lambda vs. non-lambda operating modes

[EffectaBoilerUser (USA)]

By George, I think I've done it!

I've been working on getting the effecta lambda boilers tested/certified/listed to UL and CSA standards and the testing is finally completed. We should have these boilers officially listed within the next month or so.

Now for the really good stuff. I've attached a document which contains data logging results of my effect lambda boiler operating in both lambda and non-lambda modes.

As you can see from the detailed charts/data, the effecta lambda control system gets the boilers efficiency and operating ease to the next level. The biggest difference I see is the lowering of the exhaust gases by almost 100 F when the lambda sensor is used to automatically/continuously control the amount of oxygen introduced into the primary and secondary burn chambers throughout the entire burn (approx 4.5 hours). This lowering of exhaust gas temperatures correlates directly to an increase in the secondary burn temperatures and a more consistent burn - less ups and downs in addition to more useful BTU's into the WATER BATTERY! Simply put, more BTU's per pound of wood.

I am looking forward to the feedback I get on this detailed data. As far as I know, this is the first time that both secondary temps and flue temps have been measured for both lambda and non-lambda controlled boilers.

Happily and easily heating my home with an effecta lambda 35 in northern Michigan!

EBU

 

[jebatty]

In general a 1% increase in efficiency for each 40F drop in flue temp; 100F drop in flue temp = about 2.5% increase in efficiency.

 

[pwschiller]

That 1 percent change in efficiency per 40 degree change in flue temp may be true at a certain point along the possible spectrum of flue temps, but then it can't be a linear relationship. If the flue temp was the same as the intake air you would be at 100 percent efficiency, right? But if your flue temp was 1000 degrees higher than the intake air temp, I don't think you would be running at 75 percent efficiency.

 

[jebatty]

Certainly true, and that's why I said "in general." I didn't go back and look at the underlying study, but I will assume for now that the flue is within a "normal high" operating range, maybe in the 500-600F range, and then a 100F drop in flue temp is realized.

 

[ewdudley]

That 1 percent change in efficiency per 40 degree change in flue temp may be true at a certain point along the possible spectrum of flue temps, but then it can't be a linear relationship. If the flue temp was the same as the intake air you would be at 100 percent efficiency, right? But if your flue temp was 1000 degrees higher than the intake air temp, I don't think you would be running at 75 percent efficiency.

Achieving 100% efficiency with ambient temperature flue gases assumes that the wood is perfectly dry and that the water vapor products of combustion have been condensed out of the flue gases so as to recover their heat of vaporization.

A realistic reference point might be a non-condensing boiler with 20% MC fuel achieving a little better than 80% efficiency with 400 degF flue gases. If the unit were perfectly inefficient the flue gases would be about 3600 degF, which gives a 1% drop in efficiency per 40 degF increase in flue temperature.

--ewd

 

[ewdudley]

As you can see from the detailed charts/data, the effecta lambda control system gets the boilers efficiency and operating ease to the next level.

Actually I can't see much from the detailed charts/data, they are illegible for the most part. Maybe I need a better internet connection.

The biggest difference I see is the lowering of the exhaust gases by almost 100 F when the lambda sensor is used to automatically/continuously control the amount of oxygen introduced into the primary and secondary burn chambers throughout the entire burn (approx 4.5 hours).

Very interesting. How, exactly, does optimizing the stoichiometry of the combustion process lower the flue gas temperature?

I am looking forward to the feedback I get on this detailed data. As far as I know, this is the first time that both secondary temps and flue temps have been measured for both lambda and non-lambda controlled boilers.

Sorry, I'm not seeing the detailed data part. To me what would be interesting would be a couple of runs performed, with and without lambda control, according to the BBMCP (Ballenthin Batch Mode Calorimetry Protocol):

-Start with a know quantity of wood with a known moisture content.
-Instrument system with a few temperature measuring devices. Boiler return and supply, plus tank top and bottom should be sufficient.
-Account for the water volume of the boiler, plus the water volume of storage. Optionally account for the steel in the tanks and the boiler.
-Override the storage circulator and bypass return temperature protection device for a while until all temperature sensor readings are reasonably consistent. Average the starting temperatures and record as beginning system temperature.
-Burn the wood with no load being drawn from storage.
-Again override the storage circulator to mix the system. Average the ending temperatures and record as ending system temperature.
-Calculate the heat gained by the system and divide by the LHV of the fuel supply, to yield efficiency.
-Optionally estimate heat loss rate from storage and account for it.

--ewd

 

[pwschiller]

I found what seems to be a very good paper on combustion analysis, free air, efficiency calculations, etc.: http://www.tsi.com/uploadedFiles/Product_Information/Literature/Handbooks/CA-basic-2980175.pdf

The paper discussed a variety of fuel types, including wood, although most of the graphs show data using fuel oil. On page 12 there is a chart showing efficiency burning fuel oil for Net Temp (stack temp - supply temp) vs CO2%/O2% of the exhaust gases. Just as an example, for a net flue temp of 380 F vs. CO2% = 13.4% & O2% = 3%, the graph shows an efficiency of 85.4%. At a constant CO2%/O2%, the efficiency does indeed show a decrease in efficiency of about 1% for each 40 F jump in net flue gas temp.

But, what the chart also shows is that increasing the excess air has an even greater effect on the efficiency. At a net stack temp of 500 F and O2% = 3%, the efficiency is 82.7%. Raising the O2% to 8% by increasing the amount of excess air decreases efficiency by an additional 3.7%. The lambda controlled boilers are able to maintain the CO2%/O2% within a very tight range throughout the entire burn cycle so that efficiency is maximized. I'm sure that many of the non-lambda gasifier owners have their air intakes set to achieve high efficiency while the bulk of the wood is being burned, but there are also people who probably have O2% in their exhaust gases that's far, far in excess of where it optimally should be, and their flue gas temps aren't necessarily indicative of what efficiency they are running at.

I understand wood as a fuel is quite different than fuel oil, due to water in the wood and elements that don't contribute to combustion, but I think that the chart makes an important point about having the appropriate amount of excess air, which may be hard to determine if you don't have an O2 or CO2 sensor, or unless you run a series of weighed wood vs. net BTU/calorie tests like Eliot is recommending.

 

[DaveBP]

And as long as the curmudgeons have the stage, just for simplicity and purity of analysis, how about a run or two with oven-dried wood just to remove that one variable?

 

[EffectaBoilerUser (USA)]

Thanks everyone for the feedback!

I think we are at the point where we are starting to "spit hairs" and obviously everyone has their own opinion with regards to how much temperature change directly effects efficiency.

I think there are so many variables which come into play that we could spend the rest of our life trying to determine/measure every last portion of 1%.

Thus, I am very happy with the results of my effecta lambda 35 boiler. I have been on hearth for a few years and have yet to see the type of data that I am measuring/posting on the forum.

Common sense tells me (and I hope everyone else on hearth) that a decrease in the flue gas temperature MUST result in an increase in the usable BTU's into the water. The laws of physics tell us that energy does not disappear but rather changes form or moves to different locations.

So, if we can lower the chimney exhaust temperatures by approx. 100 F (or 25%) I know that I am able to convert a good portion of this reduced chimney temperature into usable BTU's to heat my house/hot water.

Having operated my effecta lambda 35 boiler for 900 hours of operation (and having been a previous owner/operator of an EKO40 boiler for three years) I can honestly state that there are many more benefits to having a lambda control system than just an increase in efficiency. For example, not having large quantities of smoke in your face/house, not having to free up a stuck by pass lever, not having to spend countless hours to continuously make manual changes/modifications to the primary and secondary draft openings in an effort to achieve optimum efficiency are just a few of the benefits of the effecta lambda 35 boiler/lambda control system.

PLUS, I feel real good knowing that I am operating one of the most efficient and easiest to use wood gasification boilers available in the world today. Anyone who has researched the energy policies and wood harvesting policies of Sweden must know hat Sweden has some of the most stringent laws in the world. For example, not allowing the effecta lambda 35 boiler to "cycle" - turn the fan on and off depending on water temp. in the boiler is an example of this.

Last summer I traveled to Kungsbacka Sweden to meet with effecta and also attended the world energy fair in Sewden. It was at the world energy fair that I realized that Sweden is one of the most forward thinking/creative countries in the world when it comes to alternative/renewable energy technologies. Unlike the government of the US that does not "walk it's talk" (which is evidenced by the much lower federal tax credits for 2011- biomass buring devices dropped from $1,500 to $500), Sweden is very committed at all levels of government to "walk the talk".

I will continue to data log my effecta lambda boiler using different scenarios that have been suggested and will post my results on hearth.

Thanks for all the feedback both now and in the future!

EBU

 

[woodsmaster]

I'm not yet convenced that lower flue temp means higher efficency. I can turn the fan speed down wich will lower flu temp ,BUT the fire takes longer to burn therfor there could be just as much heat going up the chimminey only taking longer to do so ?

 

[shortline]

And as long as the curmudgeons have the stage, just for simplicity and purity of analysis, how about a run or two with oven-dried wood just to remove that one variable?

Plus weighed to the quarter ounce and same species certified! To remove a couple more.

 

[TCaldwell]

Besides the obvious,lower flue temp/higher effiency through heat exchange, What o2 control does is to maintain the residual o2 content to a stiometeric or optimum fuel air ratio. by maintaining this approx 7% ratio the secondary burn temps are not as high as they would be at 4% residual o2 in the flue stream, consequently the resultant flue gas temps are lower for the stiometeric burn.

 

[shortline]

"Process heating equipment almost never runs stoichiometric. Even so-called "on-ratio" combustion, used in boilers and high temperature process furnaces incorporates a modest amount of excess air - 10 to 20% more than needed to burn the fuel completely.

If insufficient amount of air is supplied to the burner, unburned fuel, soot, smoke, and carbon monoxide are exhausted from the boiler. The results is heat transfer surface fouling, pollution, lower combustion efficiency, flame instability and a potential for explosion. To avoid inefficient and unsafe conditions, boilers normally operate at an excess air level. This excess air level also provides protection from insufficient oxygen conditions caused by variations in fuel composition and "operating slops" in the fuel-air control system.". http://www.engineeringtoolbox.com/fuels-combustion-efficiency-d_167.html

Traditionally home heating with wood has used the fuel rich combustion sinerio were we have limited the amount of air to control the rate of heat production. The beauty of central heating with a boiler is that it is not out of possibilty for many homeowners to add water storage to enable biomass boilers to burn a load of feedstock at optimum fuel-air ratio for the most efficient consumption. Gasification biomass boilers are very good at optimizing feedstock consumption, but in the early going seem to have focused more on the control fuel induction to the boiler. To my mind the better way to automate this process of biomass burning is to control the induction of air to insure complete "effiecient" combustion. This Is what interests me so much in effecta's lambda control of the gasification process in their wood boilers.

Although the measurement of flue temperature is useful in understanding the rate of heat transfer, I think it is small part of the bigger picture of fuel efficiency in a boiler.

 

[TCaldwell]

Shortline, this is a more wood pertinant short explanation, confirming the 7+/- % o2. google theory of wood firing , the one to the videncenter link.

 

[ewdudley]

Besides the obvious,lower flue temp/higher effiency through heat exchange, What o2 control does is to maintain the residual o2 content to a stiometeric or optimum fuel air ratio. by maintaining this approx 7% ratio the secondary burn temps are not as high as they would be at 4% residual o2 in the flue stream, consequently the resultant flue gas temps are lower for the stiometeric burn.

Diluting the flue gas with excess air above optimum lambda will necessarily lower the flue temperature. With constant fuel gas flow, lowering excess air away from greater-than-optimum lambdas towards optimum lambda will increase flue temperature.

Efficient reduction of flue gas temperature requires that the rate of combustion be reduced while maintaining optimal lambda, such that the area of the heat exchange surfaces becomes relatively greater and more effective. The OP's graphs, such as they are, do nothing to establish that efficient reduction of flue gas temperature has been accomplished.

--ewd

 

[DaveBP]

What we need is a reasonably accurate way to measure the flow rate of the flue gas, as well as its temperature.

Otherwise we don't know how much energy is being lost to the atmosphere any more than we know how much energy is flowing through a pipe by its temperature alone.
Gotta have those Gallons-per-Minute figures to undertstand what's happening.

Maybe Pounds-per-Minute would be a more useful figure for flue gas.

 

[pwschiller]

What we need is a reasonably accurate way to measure the flow rate of the flue gas, as well as its temperature.

Otherwise we don't know how much energy is being lost to the atmosphere any more than we know how much energy is flowing through a pipe by its temperature alone.
Gotta have those Gallons-per-Minute figures to undertstand what's happening.

What the sensor and controls on these boilers do is maintain a relatively constant excess O2% in the exhaust gases. In the case of the OP's graphs above, he has his boiler set to maintain CO2 = 13% in the exhaust gases, which results in O2 of approximately 3.5%, which means that there's roughly 17% excess air introduced above what is needed for complete combustion. If we know the temp in the secondary chamber, the temp of the flue gases, and the percentage of excess air that is diluting the products of combustion & intake air gases that aren't involved in combustion, we can get calculate a pretty decent estimate of the efficiency, assuming that we are getting good mixing of gases and nearly complete combustion. The link to the paper that I provided in a posting above explains it far better than I could.

I may be wrong, but I think what Eliot is questioning is whether the boiler is actually doing what it was designed to do, which is maintaining a fairly constant percentage of excess air throughout the burn cycle, since CO2% or O2% is not shown on the graphs.

 

[ewdudley]

I may be wrong, but I think what Eliot is questioning is whether the boiler is actually doing what it was designed to do, which is maintaining a fairly constant percentage of excess air throughout the burn cycle, since CO2% or O2% is not shown on the graphs.

And it is fair to question, after all.

For instance I used to have a hand in designing control systems that had a humidity sensor input that could be used to control humidification/dehumidification of the controlled space. Depending on the temperature and actual RH of the air, the accuracy guaranteed by the manufacturer of the sensor could easily be no better than plus or minus four percent RH.

But once that input had been measured with a twelve bit AToD, and had been logged in the data recorder with 0.01% resolution, it was shocking to witness the amount of faith otherwise rational people would invest in such a number.

Garbage-In plus digital display equals Gospel-Out.

It's perfectly normal and acceptable to publish this kind of nonsense as a marketing device. Separating fools from their money can be fair and honorable since fools don't need to distinguish between the truth and what they choose to believe, and thus true value can be derived from nonsense.

But I would prefer bona-fide measurements that would enable me to quantify the putative economic and operational advantages and weigh them against the increased capital expense. So again, a good starting point would to measure how much wood goes into the firebox and the MC of that wood, and then measure how much energy was captured into storage.

--ewd

 

[pwschiller]

And it is fair to question, after all.

Yes it is.

So again, a good starting point would to measure how much wood goes into the firebox and the MC of that wood, and then measure how much energy was captured into storage.

Unless it was done by an independent lab or someone you personally knew and trusted, wouldn't you still question the actual weight, moisture content and species of the wood?

I would be pretty happy to just verify what the boiler was reading for O2%/CO2% with another analyzer: (broken link removed to http://www.instrumart.com/Product.aspx?ProductID=30968)

I should probably add that the analyzer should also check for products of incomplete combustion.

How do you think that the new Central Boiler models would compare? They claim that the E-Classic 3200 has an efficiency rating of 97%!

 

[ewdudley]

So again, a good starting point would to measure how much wood goes into the firebox and the MC of that wood, and then measure how much energy was captured into storage.

Unless it was done by an independent lab or someone you personally knew and trusted, wouldn't you still question the actual weight, moisture content and species of the wood?

I'd just like useful test information, preferably developed using procedures and measurements that are reliable and repeatable in the field so we can compare results and try to identify the reasons that one test varies from another.

Fortunately the btus per pound of wood dry matter is supposed to be remarkably consistent. Moisture content is trickier, but that shouldn't stop someone from reporting what they measured and how, and the reader can take it from there and decide what jibes and what sounds too good or bad too be true.

I would be pretty happy to just verify what the boiler was reading for O2%/CO2% with another analyzer:

That would go a long way towards convincing me that the unit is doing what it claims to be doing. Then it would be possible to compare against the flue gas profile of a well-tuned non-closed-loop unit and come up with real world measurements of typical excess air and then estimate the economic impact to the operator.

(broken link removed to http://www.instrumart.com/Product.aspx?ProductID=30968)

Wow, I'd still probably rely on my burner guy to tune the boilers, but at that price it would almost be worth it to get one to take some measurements to see what affects what.

How do you think that the new Central Boiler models would compare? They claim that the E-Classic 3200 has an efficiency rating of 97%!

And there you have it. And they said America had lost its competitive edge, but now we see that ingenuity and know-how are alive and still kicking!

 

[TCaldwell]

Eliot, given that the hx capability remains the same , graph from the same boiler, the draft inducer is one speed, the heat load is off , the only variables would be wood load and water starting temps. this primarily refers to heat exchange capability, not combustion effiency. The closer to and length time you can maintain 7 decides how combustion efficient your boiler is period. how your boiler handles the 7% fluegas is system effiency, and most boilers as you know vary in their ability. two boilers running at 7%o2 , the one with the lower flue temp at the end of burn will have put out more btus than the other one. Really brian needs to datalog the o2% for a closed loop burn and a open loop burn to put a end to this.

 

[TCaldwell]

pete, 7% o2 calculates a co2 value of 13% for cordwood with a 20% mc based on the fuel factor for wood

 

[pwschiller]

pete, 7% o2 calculates a co2 value of 13% for cordwood with a 20% mc based on the fuel factor for wood

You're right. I hadn't noticed that the paper I referenced gives a CO2 max of 19.1% for dry wood, back in one of the appendices. That puts the ratio much closer to what you wrote above. Do you have a reference that shows CO2 max at at different MCs?

 

[TCaldwell]

Pete, google co2 max calculations for wood combustion, check out the qlimited one