Idiot Proofing Gasifier Operation

[jebatty]

I think inexperienced operator proofing a gasification boiler system can be very simple. It requires sufficient storage to make sure 1) the boiler never idles and 2) the boiler never experiences overheat and shuts down or boils over, plus 3) having dry wood of the appropriate split size. Assumed, of course, is that the system is properly designed, including water flow sufficient to handle boiler output.

The Garn comes close to this with its relatively large storage tank, as it does not idle, unless it experiences low water shutdown, but it can be overheated through loading when the tank and demand cannot accept the wood load output. Overheating results in boiling off excessive btu's.

Deep Portage has come closer than I have even seen to inexperienced operator proofing a gasification boiler system. It operates both a Garn WHS 3200 and a Wood Gun E500, together with a 4000 gal storage tank, each boiler having real world output in the range of 500,000 btuH, to heat a 56,000 sq ft facility.

While some staff is experienced, most staff is not, and instructions for staff operation are as simple as A) check to see if wood load has mostly burned out, and if it has ... B) check one digital temperature gauge to see if it is less than 160F; C) if less than 160F, either or both boilers may be loaded with 10-12 splits of wood (this amount weighs about 100 lbs); D) with this wood load the storage (4000 gal + Garn 3200 gal), even if no demand, will accept the full output of both boilers without overheating and without any Wood Gun idling; E) if the digital temperature gauge is 160F or above, do not load either boiler. DP has never experienced a system overheat or Wood Gun idling under this operating procedure.

The DP system is primary/secondary piping. The Garn is piped to the primary via a plate hx. The Wood Gun is directly piped to the primary, with return water protection. In addition to two large loads on the primary, a 4000 gal storage tank is piped to the primary as a third load. This storage tank has a sensor at the 4000 gal tank midpoint which outputs to the digital temperature gauge mentioned above. If the Garn alone is operating, its output supplies the primary to meet system demand, if any, and to charge its internal 3200 gal tank plus the 4000 gal storage tank. If both the Garn and the Wood Gun are operating, same result, but if the Garn water temperature is less than the primary loop/storage tank temperature, then the plate hx operates in reverse to heat the Garn, along with Garn output, from the primary loop. If only the Wood Gun is operating, then its output supplies the primary to meet system demand, if any, and to charge both the 4000 gal storage tank and the Garn 3200 gal storage tank.

Inexperienced operators are not responsible for any cleaning or maintenance on these boilers. The inexperienced operators only "load, lock and fire."

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It also is possible to come close to inexperienced operator proofing a gasification boiler with storage by using weighed wood burns, but weighing wood would need to be made easy for the operator. The operating procedure would be: A) check to see if wood load has mostly burned out, and if it has ... B) read one digital temperature gauge; C) look at a prepared chart to see how many pounds of wood should be loaded in the boiler based on the gauge temperature reading; D) weigh wood as shown by the chart and load the boiler.

For my system with 1000 gal of storage, I also use a sensor and digital temperature gauge which reads tank temperature at the midpoint. I have a chart with tells me how many pounds of wood to load based on that temperature. I prepared the chart based on 190F ending tank temperature and no system demand. With a 1000 gal tank, and at my boiler efficiency, I know that I need 1.7 lbs of wood to raise the tank temperature 1F. If the temperature gauge reads 130F (desired tank end point temperature = 190F), I simply weigh out and burn 102 lbs of wood.

I built a simple hanging platform with a digital luggage scale for my wood weighing. Look at *bay and you will find these scales for less than $10.

 

[infinitymike]

Thanks Jim,
As always, informative.
Do have any pictures or drawings of the primary/secondary system and layout.
I set up a primary/secondary system to have either my WG or the oil burner heat the house.
It wasn't set up 100% correctly and really think that the way the piping is decreases my efficiency drastically.
I flipped the way the supply and return lines enter the loop and increased my efficiency by 25%
I don't know if I would gain any more efficiency if I move around the supplies and returns of the 3 zones.

 

[jebatty]

Sketch of the p/s. I did not design this layout. It works.

 

[Floydian]

Hi Jim,

Good stuff, as usual. Your informative posts were a big help in designing my system(Vedolux 37, 1000 gal. storage, low temp radiant floors). The Vedolux doesn't idle, so storage is obviously required.
I chose to have the boiler ONLY heat storage and let the loads draw off of storage as needed. ( I get usable hot water in the top of storage as soon as the loading unit is satisfied with 140)

I knew I wanted to do weighed batch burning and wanted "idiot proof" as well. So far so good after a month and a half of operation. This system just works-really well!

For my system with 1000 gal of storage, I also use a sensor and digital temperature gauge which reads tank temperature at the midpoint. I have a chart with tells me how many pounds of wood to load based on that temperature. I prepared the chart based on 190F ending tank temperature and no system demand. With a 1000 gal tank, and at my boiler efficiency, I know that I need 1.7 lbs of wood to raise the tank temperature 1F. If the temperature gauge reads 130F (desired tank end point temperature = 190F), I simply weigh out and burn 102 lbs of wood.

I recall a post of yours where you mentioned using the PSI to determine overall system temp and when to re fire and how much wood. Just curious if you have played with this approach in your calculations?

For my system, I am seeing that 1 psi =9.2 =76,700 btus=17.3 lbs of wood. Seems to be pretty accurate once I figured the relationship between avg system temp and psi for my system.

Thoughts?

Noah

 

[dogwood]

Jim, would you mind posting your chart? I bet we could use it with little adaptation, having a Tarm boiler and 1000 gallons storage like you. Thanks. I've worked some of your ideas into my system design as well. So thanks again.

Mike

 

[bigburner]

curious, what is the difference in the RW temp of the WG when the Garn is off line verse when they both operate.

 

[jebatty]

Here is a simple chart based on 1000 gal of storage and 1.7 lbs of wood to raise the tank 1F. This assumes boiler efficiency in delivering btu content of wood to water storage at about 82% based on the formula of 6050 btu/lb of wood at 20% MC and 400F stack temperature. Delta-T is the difference between storage tank target charge temperature and mid-point storage tank temperature. This also assumes you are charging a storage tank with the boiler and with no other load on the system. Try this to see how it works and adjust as necessary.

With my system, if I experience a load on the system during charging, I also have learned that a system draw on storage will drop tank temperature 10F, so I increase my Delta-T by 10 to account for this system draw (or simply add 17 lbs of wood to the weight of wood specified by the chart). My draw on storage is very consistent because I only am heating a radiant floor, which I maintain at 61F and differential of 1F. The result is that when the floor drops to 60F, draw on the storage begins, and the floor ends up at 62F at the end of the draw (it overshoot a little).

WOOD LOAD CHART
 
Delta-T    Lbs. Wood
90            153
80            136
70            119
60            102
50             85
40             68
30             51
20             34

 

[jebatty]

what is the difference in the RW temp of the WG when the Garn is off line verse when they both operate

There is no difference. Return water protection for the WG is via a motorized 3-way mixing valve with a Tecmar controller. It is set to maintain 160F return water temperature.

 

[Nofossil]

While I REALLY hesitate to use the term 'idiot proof', I'm a big fan of 'user friendly'. For the wiser and more feminine portion of our local user community, 'user friendly' is a big factor. I have a gauge panel on our internal home page that provides a simple view of what's happening:

Directions are pretty simple (but probably could be even better):

1. If Tank kBTU is in the yellow, you'll want a fire pretty soon.
2. If you have a fire going, add wood when combustion drops into the yellow.
3. If Tank kBTU is past 3:00 (about 300kBTU), don't add any more wood.

Adding wood is pretty simple, and I have pictures and a checklist on the wall:

• Turn off fan (labelled switch on front panel)
• Open damper
• Open door
• Fill about halfway with splits
• Close door and damper
• Turn on fan

Starting a fire is more complicated than I would like, but even that usually goes pretty well.

 

[maple1]

Storage has taken practically all the 'user-unfriendly' potential out of my system.

As long as my top storage temp (actually measured at the middle of the top tank) is no higher than 165 or so, I feel pretty safe in just loading it up & letting it go. If it does get up there a bit too far in temps, it will just dump some to the house anyway - and my boiler has no fan & also can't idle, so that part is out of the 'unfriendly' side of things too. The main thing I have to watch out for now on the 'unfriendly' side is if bridging occurs on a cold light-up. It happened today actually, for the first time in a while. As long as someone looks outside once in a while, they'll know to give the fire a poke if they see smoke drifting in the air - I was kind of surprised at how much smoke that bridging can create.

That's in heating season, so the house is usually drawing some heat off too - I might have to adjust my practices a bit when I get to 'DHW only' season.

 

[BoilerMan]

NoFo, I like the border around the gauges! The feminine part of my household would like to look at that too!

TS

 

[infinitymike]

jim,
would there ever be a need for the WG, Garn and storage to supply hot water at the same time?

 

[Fred61]

• Turn off fan (labelled switch on front panel)

I don't shut off the fan when checking the fire or re-loading. Probably doesn't benefit in an way except I feel better when I don't hear the fan motor spooling up so slowly. I have the fan speed set at 50% so the starting torque pretty low.

 

[jebatty]

would there ever be a need for the WG, Garn and storage to supply hot water at the same time?

I think the answer certainly is "yes," but I don't know at what outside temperature this is likely to occur. The Garn itself can meet DP's demand down to about 12F outside temperature, and the WG alone down to something arround -10F. Certainly at some low temperature both the Garn and the WG, total combined output about 1 million btu's, would be insufficient to meet demand, and with both boilers burning, tank temperature would also be dropping, which means that the tank also would be supplying btu's to meet demand.

While I REALLY hesitate to use the term 'idiot proof'...

I used the term as an attention grabber, and then in the post talked about the inexperienced user. No intent to offend or diminish the efforts of anyone. But if I did, I apologize for that. Please accept the post for the merit of its content, if any.

 

[infinitymike]

I think the answer certainly is "yes," but I don't know at what outside temperature this is likely to occur. The Garn itself can meet DP's demand down to about 12F outside temperature, and the WG alone down to something arround -10F. Certainly at some low temperature both the Garn and the WG, total combined output about 1 million btu's, would be insufficient to meet demand, and with both boilers burning, tank temperature would also be dropping, which means that the tank also would be supplying btu's to meet demand.

Then why have two monster units like that?

 

[jebatty]

Then why have two monster units like that?

The easy answer is that temps in the -40'sF are not unusual here. Temps have even gotten into the -50'sF, and that's not windchill, but real temperature. Two boilers are needed, plus storage, when the cold really settles in.

A more complete answer is that DP acquired both boilers to fulfill part of its educational mission. Try different technology, test in real world conditions and report. As past reports have shown, the Garn cannot operate on a continuous burn basis. It's design is intended for batch burn operations, drawing from storage between burns. The Garn feasibly could operate continuously for about 18 hours at 100 lbs of wood per hour, and then the Garn had to be allowed to burn out and shut down so that ash and coals could be removed. Heat still is needed during these shutdown periods, thus the WG.

The WG can operate continuously for an extended period of time, but its high output in excess of demand and without storage caused it to idle, from which it would awaken with a small explosion. The 4000 gal of storage was added primarily to serve the WG, and now the WG always can burn full out, efficiently and no idling, like most other gasifiers with storage. And the storage then can meet demand between firings when continuous firing is not needed.

In addition, two boilers means that even if one boilers goes down, the other is available to meet critical demand and prevent freeze up. A backup plan always is needed in a large facility.

I did extensive testing and reporting a couple of years ago. If you search for "WHS3200" or "E500" you should be able to locate those long threads and get an even more complete answer as to how and when these boilers are used and pluses and minuses of each.

 

[infinitymike]

The easy answer is that temps in the -40'sF are not unusual here. Temps have even gotten into the -50'sF, and that's not windchill, but real temperature. Two boilers are needed, plus storage, when the cold really settles in.

A more complete answer is that DP acquired both boilers to fulfill part of its educational mission. Try different technology, test in real world conditions and report. As past reports have shown, the Garn cannot operate on a continuous burn basis. It's design is intended for batch burn operations, drawing from storage between burns. The Garn feasibly could operate continuously for about 18 hours at 100 lbs of wood per hour, and then the Garn had to be allowed to burn out and shut down so that ash and coals could be removed. Heat still is needed during these shutdown periods, thus the WG.

The WG can operate continuously for an extended period of time, but its high output in excess of demand and without storage caused it to idle, from which it would awaken with a small explosion. The 4000 gal of storage was added primarily to serve the WG, and now the WG always can burn full out, efficiently and no idling, like most other gasifiers with storage. And the storage then can meet demand between firings when continuous firing is not needed.

In addition, two boilers means that even if one boilers goes down, the other is available to meet critical demand and prevent freeze up. A backup plan always is needed in a large facility.

I did extensive testing and reporting a couple of years ago. If you search for "WHS3200" or "E500" you should be able to locate those long threads and get an even more complete answer as to how and when these boilers are used and pluses and minuses of each.

And to think thats the easy answer

How many lineal feet is the loop that everything ties into?

 

[jebatty]

How many lineal feet is the loop that everything ties into?

Not exactly an answer for the Q you asked, but maybe info that's good enough.DP has been on a mission to eliminate use of fossil fuel (LP), and it nearly has accomplished this mission with its WG and Garn boilers (also a Froling for a separate structure). LP for heating now serves solely as emergency backup.

DP's main structure has an old and a new part. The old part was served by 3 sequenced LP boilers, and the new part by 5 sequenced LP boilers. A new building was constructed to house the WG and Garn, plus interior wood staging and shop space. The contractor simply "series" plumbed the supply from the wood boilers into the LP boilers. The LP boilers are still in place and available for emergency backup. Somewhere I have notes on lineal feet in the loops, but I didn't quickly locate those notes. Suffice it to say that the system will take everything that both the Garn or WG can deliver, but not everything both will deliver when operating simultaneously, except in extremely high demand situations, and during milder weather not everything that either separately will deliver. Thus, the primary reason for the added 4000 gal storage tank: end WG "puffing" and idling, and secondary reason to provide the system with btu's between firings of the boilers.

Based both on calculated pump head and taking differential pressure readings off the circulators, plus delta-T on S/R, I was able to determine actual flow rates and btu output rates for both the WG and the Garn under DP operating conditions. The threads of my previous reporting showed this. On a continuous burn basis, the Garn's output to the system was at the rate of about 500,000 btuH over an 18 hour period, although it is rated greater than this, and I suspect can meet its rating if measured on a batch burn basis. The WG is rated at 500,000 btuH, and can meet this rating on a continuous burn basis. I did not push the WG to its maximum output on a continuous burn basis during my tests, although it is clear to me that the WG as plumbed at DP can exceed its 500,000 btuH rating on a continuous burn basis. I also did not determine how long "continuous" would be, but the WG showed no evidence of reaching that maximum during an operating period similar to the Garn.

With the added 4000 gal storage tank, operation at DP of the Garn and the WG is about as simple and trouble free as wood boilers can be. These are beasts, inexperienced staff operate the boilers (load wood and walk away), staff also can cold start both boilers when needed, but an experienced maintenance person cleans and services the boilers as needed to keep them in top operating condition.