Fire Brick for grates

[danno]

I made new grates out of fire brick this season - drilled 3 3/4" holes in each brick. After I have been boiling for an hour or two, I have to run a rake under the coals to try to clear the holes - the holes are plugging with ash. I'm running 1100 cfm under the grates so I thought I would have plenty of air to keep the holes from plugging - but it's not the case. I have to rake about every 45 minutes to an hour to keep temp up.

I also think 3/4" holes are not big enough - I think it's restricting air. Anybody have similar problem, or had better success with 1" or 1 1/2" holes?

[RileySugarbush]

Most of the blowers on evaporators do not put out much flow when there is a restriction on the outlet like too tight a grate. The 1100cfm rating is likely without any back pressure. It the grate openings are too small, the flow rating goes way, way down. Sometimes the blower specs will give ratings into different output pressures as a reference. Blower designs can be optimized for best performance at a given pressure, so there are some that would work better than others in this application.

It does sound like your grates are too restricting. I use a much smaller squirrel cage blower on a grate welded of steel angles, V's pointing down like this:

VVVV

The gaps between the Vs are a bit over a quarter inch, so not a lot of area, but probably more than yours. Once the V's fill up, there is never any more ash. Virtually none in the pit and the grates stay open.

I can see how round holes could be more easily blocked so that they have near zero flow in that hole, allowing the coal to survive long enough to get covered and totally block that hole. With the slots, it is unlikely to totally block one, so the air going by the coal will burn it up quick, freeing that area.

[WESTVIRGINIAMAPLER]

I am running same type of setup with firebrick and a 745 cfm blower and I have no problem with my grates plugging up and I have aprox 20 to 22 holes that are 3/4" or less in diameter even when I boiled for 16 hours one day.

You may have too many holes for the blower to keep the holes clear. How many holes do you have??

[danno]

16 bricks, 3 holes each = 48 holes. I'm thinking I need bigger holes - you're thinking I have too many. I thought I remember that you put 4 3/4" holes in each brick?

I know with my old steel grates allowed allot more air through - too much I thought. Due to warping, I had hot embers and burning wood falling through into the ash pit.

[MapleME]

danno, what did the bricks cost you vs a new grate?

[Amber Gold]

Bricks are about $1.50 each and would take about 40 bricks. Grates are $35+ each and 4 or 5 are required for a 2x6. Bricks are cheaper...by a lot.

[RileySugarbush]

You have less total open area with your holes (21 sq. in.) than I have in my grate (28 sq. in.) with the 200cfm blower on a 2x6. Plus there is more flow friction with the long holes through the bricks.

I think you are restricted on the grate and should have more holes. You might be choking off the blower some so it doesn't put out full flow.

Of course Brandon has less area yet and he has good success. Maybe its a different type of blower?

[802maple]

Danno-

I am the one that started using this system.
Do your bricks cover the whole area that your old grates did? If not you might need a few more. I always used 3/4 inch holes and never had any problems, but I also use a high pressure blower with about 700 cfm's for a 3x10. If you have a regular squirrel cage blower your restriction loss will be much more than a high pressure blower of half the cfm's as the blower will neutralize itself in a squirel cage.

[MapleME]

Bricks are about $1.50 each and would take about 40 bricks. Grates are $35+ each and 4 or 5 are required for a 2x6. Bricks are cheaper...by a lot.

a 2x6 requires 4 or 5 grates?

[Amber Gold]

I think so...not positive becuase I have forced draft grates and onluy 2

[KenWP]

Are you putting the bricks tight toghether or spaceing them a bit also. A crack between the bricks would increase you air flow a lot.

[WESTVIRGINIAMAPLER]

I have 3 holes in my bricks and I have four rows of bricks running lengthwise in the evaporator and the first brick in each row doesn't have any holes and the rear brick only has one which only leaves 28 holes total in the four rows and I have at least one or two of those holes in each row plugged with ceramic blanket trying to move the fire around and make it burn the most effectively. All around the outsides of the brick I have it stuffed tight with ceramic blanket to completely seal off anything and prevent any air loss. I acutally had two pieces of angle iron welded together to for a "T" between each row of bricks which further helps to seal off the bricks.

[RileySugarbush]

Brandon and Danno,

Do you have the performance curves for your blowers? It would be interesting to compare their performance at various loads.

Here is the data for mine. This blower does a pretty good job of creating flow as the back pressure rises. Not all will. Some have flow drop off very quickly as they are restricted.

Note: 0.5 in SP refers to half inch of water head static pressure, equal to less than 0.02 psi!

[danno]

Thanks for all of your responses - I'm using a squirrel furnace blower. I have to run her as hard as I can to get my stack temp to 650. I use an external thermo on the stack. Last year with my open grates - I could get up to about 750 - but I had wood and embers falling through the grates suffocating in the ash pit. Used to haul out buckets of ash.

I also put air over the fire this year - which may be causing the lower stack temps. I also left very little room under my flue pan, and I'm wondering if ash has filled in that area and is choking the draft a bit.

Overall, rig is running fine, just trying to increase evap and use less wood like everybody else.

[WESTVIRGINIAMAPLER]

Sounds like something is wrong with your blower or else you are losing a lot of air around cracks in the bricks, around the outside, etc. I have 28 holes in my brick grates that are 3/4" diameter as I counted them yesterday and I run stack temps from 1400 to 1650 and these are measured internally and average 60 to 65 gph and this includes startup and shutdown and I am running a 745 cfm squirrel cage blower.