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This building becomes available after you have learned the Pyrolysis 2 (Skill) skill.
- Requires Pyrolysis 1 skill
- Requires 84 Wood to start a batch.
- Requires additional Wood and Water to add during the process.
- Upon successful completion of the burning process, yields 100 Charcoal.
- Has a Regulator.
In a Charcoal Hearth (and Oven, which works similarly), a quantity of wood is converted to charcoal through steady heating. The overall goal is to maintain the heat long enough, and hot enough, to carbonize the wood. Too much heat and oxygen, and your wood will catch fire and burn up; too little and your fire will snuff altogether.
Regulator - Charcoal Hearth only
The regulator appears to control the amount of random shift in the hearth's behavior; increasing the regulation reduces the randomness and increases the time between ticks (allowing you more time to respond). Try starting with the hearth set to no more than 2. If you have problems, increase the regulation a step or two, and try again. With some experience, you should be able to make the hearth work most of the time with no regulation. Regulation is excellent for controlling randomness when running multiple hearths (4+)and with patience you can succeed with efficiencies less than 2:1 without using any water (except to speed cooling to take your cc and start again faster).
You cannot change the regulation once the hearth is running, so make sure it's set where you want it before you start.
Display and Controls
When you press the "Begin" button, the display immediately changes to six horizontal bar scales: Heat, Oxygen, Wood, Water, Danger, and Progress. Here's what they mean:
- Heat: Heat level of the fire. If this goes to zero, the fire goes out.
- Oxygen: Controlling oxygen is important to maintaining heat. If it goes to zero, the fire goes out.
- Wood: How much wood is left in the hearth.
- Water: How much water is left in the hearth.
- Danger: When this bar reaches the right hand side (100%), your wood erupts in flames, and ruins the charcoal batch.
- Progress: How close you are to finished. This bar starts at the left (0%), and grows to the right (100%). When it reaches 100%, it turns green, and you can shut down the hearth and extract your charcoal.
In addition, there are controls:
- Add Wood: Increase the amount of wood in the fire. This will remove 3 wood from your inventory per press.
- Add Water: Increase the amount of water in the fire. This will empty 1 jug in your inventory per press.
- Vent Control: Three buttons. The leftmost button closes the vent, the rightmost opens it, and the middle one sets it halfway.
Understanding Charcoal Production
Heat is what makes charcoal happen. The higher your heat level, the faster the progress bar moves, and the sooner your charcoal is done. So the first goal is to keep that heat bar as high as possible. Anything less than halfway is going to bring your progress to a crawl, and at less than a third, you'll hardly see the progress bar move at all.
Oxygen is important for controlling heat. If you don't have enough oxygen, you can't burn wood, and the heat level will drop. The specific relationship here is a little foggy, but as a rule of thumb, try to keep the oxygen bar at no less than 1/3, and no more than the heat level.
Wood is your heat source. Adding wood will increase the heat level of the hearth, provided there's enough oxygen. Adding wood also appears to make the oxygen level drop slightly. As the hearth runs out of wood, you'll see the heat level drop, and the oxygen level will shoot up, even with the vent closed.
Adding water will reduce heat levels, which is normally a bad thing. However, it also tends to dramatically reduce danger level (see below), which is definitely a good thing.
Danger level is the bar to keep a close eye on. It appears to relate primarily to heat, oxygen, and water. As your heat and oxygen levels rise, the danger bar also rises. If you add water, the danger bar tends to drop. The danger bar must not be allowed to reach 100%, or the wood combusts, ruining the entire batch.
The vent controls are the final piece of the puzzle. Closing the vent (left button) reduces the amount of oxygen in the hearth, and tends to cause a small increase in heat. Opening the vent (right button) increases the amount of oxygen in the hearth, and tends to cause heat to drop.
How to Make Charcoal
Okay, so you've got the theory, now how about the practice?
First off, get your 200 wood, several jugs of water, and charcoal hearth together. Pin the hearth, check the regulation level and set as necessary, and then click Begin.
Every tick (once every few seconds), you'll see the bars move around a little. Here's what to focus on:
Try to keep the heat bar as high as possible. Try to keep the oxygen bar somewhere between 1/3 and the heat bar. Try to keep the danger bar below 3/4 (with experience this may ride somewhat higher). Start with the vent halfway open, and work on getting the heat bar to about 2/3rds. Try to control heat and oxygen levels by adding wood or by waiting, rather than resorting to the vent controls. If the danger bar starts getting too high, add a little water, and wait. The key to the process is to act cautiously, and use some forethought ("I just added some wood, that'll make the heat go up, so I'll wait a couple of ticks before adding any more"). Above all, practice!
Losing Control The fastest way to lose control of the hearth is to add more than one of anything in the same tick. Avoid adding multiple units of wood or water to the hearth, as well as flipping the vent control from all the way open to all the way closed (or the opposite). If you're about to blow up your wood, you can try salvaging the process in this fashion, but usually it will only make things worse.
"Where'd All My Heat Go?" It is possible to get the hearth stuck in a low-heat mode. It'll have plenty of oxygen, plenty of wood, but the heat level will be very low. The progress bar won't move, and despite the fact that you're stacking wood in the hearth, it won't get any hotter. While it is possible to recover, it takes a long time, a little luck, and a lot of wood. The best bet in this case is to abandon the project and try again; you'll get 100 (hearth) / 200 (oven) wood back if you just let the hearth go out. To avoid this situation, focus on keeping that heat bar up, and don't be too quick to use the vent controls!
Vent Controls It appears that the vent has a massive effect on oxygen and a minor, inverse effect on heat. Thus, one might be tempted to close the vent in order to boost the heat, rather than adding wood (hey, the vent is free, right?). However, closing the vent actually appears to take energy out of the system; in other words, the small bump in heat levels is offset by the large drop in oxygen levels. Over time, closing the vent repeatedly will actually tend to reduce the temperature of the hearth, and can lead to the vicious low-heat cycle described above.
Stopping the Hearth Dump a lot of water (hit the button 3 or 4 times in a single tick) and open the vent all the way. The oxygen level will shoot up, the heat and danger levels will plummet, and you'll have the hearth turned off in a matter of a few seconds. This does not reduce the yield, and should not cause any increase in the danger level.
Advanced Techniques If multiple hearths are begun at the same time and wood/water/oxygen levels are adjusted together (within a tick), they will operate identically. This makes it possible to run as many hearths as you can click without having to think too hard. If you miss a beat and one hearth gets out of sync, don't panic. Keep adjusting them together and they will tend to sync up again. It is possible to complete a charcoal batch even after the fire is snuffed (as long as heat is > 50%, progress will increase still). Snuffing the fire and coasting to completion is fun ;) Danger is a combination of heat and oxygen (and water) - by keeping oxygen very low, the heat/danger can be kept very high, giving fast progress and cheaper batches. When starting a batch, try adding wood twice in the first tick. Then sit back and watch for the next 10 ticks or so as heat/oxygen move into their perfect high/low ranges like magic. Final Thoughts Practice, practice, practice. There's a lot of guesswork and instinct involved in hearth operation that cannot be conveyed without experience. Sit down with a few hundred wood, and practice making charcoal. Try forcing the hearth into certain "bad" states, so you'll better understand how to avoid them. Also, if you find something that works for you, and it's contrary to this document, don't hesitate to use it; this is based solely on my experiences and preferences, so it may not work for everyone. I just hope to help one person out there who is ready to kill their charcoal hearth.
Video Demonstration I've created a video to demonstrate how I make charcoal. I let the oxygen get a little low a couple of times when I was venting but as long as it doesn't go completely to zero, it's not a problem. Notice that I kept the heat up very high and was ready to add some water at all times. I can run 3 or 4 ovens like this simultaneously because they all seem to stay in synch if you begin the process on all of them almost at the same time, and also add the wood/water at the same time etc.
Here's another one I found, with voice-over: http://www.youtube.com/watch?v=TShFdDG6Ceo
A charcoal oven: http://www.youtube.com/watch?v=1_i_9QHsNvk