From the first lump of coal to the reactor

Before you start

Prompt Critical is about a whole industrial complex, from a coal mine to a closed nuclear fuel cycle. It has no blocks that just hand out energy. A boiler builds pressure, a mine fills with methane, a rope wears out, and a casting gets a shrinkage cavity if you forget the riser. The physics core computes all of it from real equations.

Create provides the mechanics: shafts, gears and contraptions. The mod adds what turns those shafts and what they drive: the steam engine, the mine fan, the hoist, pumps and machine tools.

How progress works

There are no research points and no tech tree. The next step is unlocked by materials. Without steel you can't make pipe, without pipe there's no oil, and without electricity there's no reactor graphite. Old industries keep running: a plant in the nuclear era still mines coal and melts steel, because everything else is made from them.

The engineering handbook

• Engineering Handbook. You get it the first time you join a world. Chapters open as you play: when you place a block, pick up an item or earn an advancement.
• Operating Procedure. Building a boiler, hoist or mine fan gives you its procedure. Put it on a Document Lectern by the plant, where anyone can read it.

The handbook explains the physics and teaches you to read instruments. It never shows your plant's live values: pressure comes from the gauge, and gas from the lamp and the methanometer.

ERA I0

Coal and steam

The first era rests on two things. Coal gives heat, the boiler turns heat into steam, and the steam engine turns a Create shaft. Everything else in I0, from the mine and coal preparation to the foundry and the machine shop, either produces coal or runs off that shaft.

1. Find coal

Coal lies in seams: flat bodies 1–4 blocks thick and 48–160 blocks long, dipping gently. Look under plains, taiga and swamps. Seams come in series, one under another, 6–20 blocks apart. The floor of a seam is usually fireclay, which you'll need later for refractory brick. Pyrite and sphalerite turn up nearby.

• Geological Map. Found in abandoned mineshaft chests, cartographers' houses, shipwrecks and dungeons. Right-click it to see the distance, bearing and depth of the centre of the nearest seam or ore body.
• Run-of-Mine Coal. What a seam drops. Each piece carries the assay of the spot it came from, shown in the tooltip. Pieces with different assays don't stack.

The assay is four numbers: moisture W, ash A, volatile matter V and sulphur S. Coal is ranked by volatile matter, and rank depends on depth (Hilt's law: the deeper the seam, the higher the rank).

Vanilla Minecraft coal works as a long-flame steam coal, so you can light your first boiler with it.

2. Raise first steam

The first boiler house is a fire-tube boiler, a chimney over it and a steam engine alongside. The engine sends rotation into the Create network. This is the first goal of the game, and it earns the First Steam advancement.

What you need

• Fire-Tube Boiler
  3×3×6, 5 MW, 1.2 MPa
• Chimney
  about 17 sections, 20 m
• Steam Engine
  3×3×5, about 119 kW
• Chain Grate Stoker
  optional

You'll also need water (a bucket or Create pipes), coal, and flint and steel, a torch or a fire charge. A pressure gauge on the front is optional, but without one you're working blind.

Why the first light-up goes wrong

A boiler doesn't draw air by itself. The chimney pulls air through the grate: a column of hot gas is lighter than the same column of outside air, and that pressure difference is the draught. A cold chimney draws poorly. Load three coal at once and the furnace runs out of air. The coal burns to carbon monoxide, black smoke pours from the chimney, efficiency drops to about 0.3, and steam takes more than half an hour. Fire with a thin bed instead, and the shaft turns about 20–25 minutes after you start with an empty boiler.

Step by step

1. Place the boiler. It goes down whole, 3×3×6, empty and cold. Leave room at the side for the engine and at the front for the stoker and gauge.
2. Build the chimney over the rear top edge of the boiler, above the flue. Height is 3 m of flue plus 1 m per section. Aim for 20 m, about 17 sections. A short chimney means weak draught and a long warm-up.
3. Place the steam engine right against the boiler. It couples to the boiler whose block it touches. Run a Create shaft to the engine's coupling. A Create wrench on the coupling picks the gear: 16, 32 or 64 rpm.
4. Fill with water. A bucket or a Create pipe into any block of the boiler fills the 4 m³ feed tank. The feed regulator fills the boiler itself in about 3.5 minutes. Don't let the tank run dry.
5. Get coal onto the grate. Right-click the boiler with coal: one item is 100 kg, up to 500 kg on the grate. Or put a stoker at the front with a Create shaft from the left, which feeds 0.3 kg/s at 32 rpm.
6. Charge one coal and light it with flint and steel, a torch or a fire charge.
7. Watch the smoke. Light smoke: add another coal. Black smoke: wait for it to clear. As the chimney warms up, bring the feed up to three coal on the grate, or 0.3 kg/s.
8. Hang the pressure gauge on the boiler front. Click the boiler with an empty hand to see the bed on the grate, the water in the tank, the furnace state and the plug.
9. Wait for 0.5 MPa, half of working pressure. The engine's stop valve starts closed: open it with an empty-hand right-click on the engine.
10. Stuck on dead centre? Sneak and right-click the engine with an empty hand to bar it over by 60°. This only works on an engine that has almost stopped.
11. The shaft is turning: First Steam. Fit a Governor Dashpot to the engine so its speed stops hunting.
12. Clear the slag now and then, with an empty hand or a hopper. Each item of Boiler Slag is 10 kg of ash.

3. Keep the boiler alive

A boiler holds 8–10 t of water. It raises steam slowly and loses it just as slowly, so it works as a heat store. It doesn't know how much steam you need. If the engine takes less than the furnace makes, pressure climbs on its own. You control pressure with the coal feed, not with the valve.

Two protections that need no electricity

• Safety valve. Built into the boiler. It lifts at 1.32 MPa with a whistle and a cloud of steam. That isn't an accident, it's a signal: cut the coal or give the engine load. Every lift is coal blown into the sky.
• Fusible Plug. A tin core in the crown of the furnace tube. If the water drops below the crown, the tin melts and a jet of steam puts the fire out. Keep a spare: they're made from copper and cassiterite, two at a time.

The engine's speed is held by a Watt flyball governor, the first automatic controller in the game. It runs about 5 % slower under load than at no load. That's normal for a proportional controller. Without a dashpot, the speed swings after every change in load.

4. Open a mine

A surface seam runs out quickly, and real production is underground. The mine starts with the first block you take out of a seam. From then on the mod tracks the air underground: how much methane, carbon monoxide and oxygen it holds, and where it moves.

Every exposed seam block gives off methane: a lot at first, then less and less over a couple of days. Broken coal gives off the rest within an hour. Methane is lighter than air and gathers under the roof: in dead ends, high spots and the cavities left by roof falls.

Ventilation

1. Put the fan in a heading mouth (3×3×3, a Create shaft from behind, 64 rpm rated). It draws air out of the mine, and fresh air comes in through the other openings.
2. Hang Ventilation Doors so the air can't short-cut to the fan and has to sweep the face. An open door short-circuits the airflow, so close it behind you every time.
3. Keep the fan running all the time while any seam is open, even with nobody underground. Once it stops, a dead-end heading reaches 1 % methane in tens of seconds, and the whole mine in minutes.

Instruments

• Canary in a Canary Cage. It senses carbon monoxide and low oxygen, not methane. If it falls off its perch, get out. Carry a living bird into fresh air and it will come round.
• Flame Safety Lamp. From 1 % methane a blue cap rises over the flame. Above 5 % the gas burns inside the gauze: leave at once. Below 17 % oxygen the lamp goes out.
• Methanometer. Right-click to measure methane at the roof. The reading turns red from 1 %.
• Mine Gas Monitoring Cabinet. Raises the alarm at 1 % methane anywhere in the mine. Click it with an empty hand for a summary of intake air, gas peaks and drainage.
• Self-Rescuer. Single use. For 30 minutes you breathe from the set, not from the heading.

Roof support

The roof holds itself up while the unsupported span is small enough. Go past the span limit and it comes down in a dome after a delay. Bigger excess, bigger dome. A roof fall blocks the heading and changes the ventilation.

A Mine Support (a timber set, 3 blocks high) adds 2 blocks to the span. Set the support first, then dig the next block. Timber rots in wet headings, and an explosion breaks it. Coal pillars between parallel headings are the most reliable support. Robbing them for extra coal is a common and expensive mistake.

5. Don't blow up the mine

Coal mine explosions nearly always come in pairs. Methane ignites, the blast wave lifts settled coal dust, and the dust explosion then runs hundreds of metres through the workings.

• Methane explodes between 5 and 15 %, worst at about 9.5 %. The edges of a rich pocket pass through that range too.
• Ignition sources: torches, lanterns, campfires, fire, lava and shotfiring. In a gassy mine, light it with Industrial Pendant Lights, not torches. A lamp in 5 % methane and an air current faster than 4 m/s blows its flame through the gauze.
• Stone dusting. A Stone Duster with Stone Dust (from calcite or diorite) spreads 100 kg per click and shows the inert fraction at that spot. Bituminous coal dust needs 60–80 % inert content. Dust regularly, because fresh coal dust settles on top.
• Explosion Barriers go across headings between the faces and the rest of the mine. You need at least 400 kg of dust per m² of cross-section, and one block holds about 500 kg.

6. Hoist and drainage

A deep mine needs two services that never stop: a hoist to move people and coal, and drainage to keep the mine from flooding.

1. Mine Hoist: a drum on a Create shaft, 64 rpm rated, up to 400 kW.
2. Headframe of 2–4 segments, in front of or behind the hoist, no more than 32 blocks away. The Mine Cage runs in the shaft under it.
3. Hang the rope: right-click the hoist with a stack of Wire Rope (10 m coils). You need enough for the shaft depth plus the run over the sheave.
4. Landings are wherever there's a way out beside the cage: two free blocks over a solid floor. The bottom one is the sump.
5. Click the hoist with an empty hand to open the panel: landing buttons, Stop, Reset trip and a speed limit up to 12 m/s.

Before each trip the hoist works out the rope's safety factor: breaking force divided by the highest tension, counting the cage, the load (80 kg per person, 300 kg per minecart) and the rope's own weight. If the factor is below the limit, the hoist won't start.

The rope fatigues on the sheave and corrodes in a wet shaft. When the panel says it's due for replacement, change it at the first stop. A rope worn to the end breaks, and the cage either lands on its safety catches or falls.

Drainage. Every ton mined opens up about a cubic metre of water, and roughly 2 m³/h more seeps in. Water collects in the sump (about 400 m³). A Mine Drainage Pump on a Create shaft moves 100 m³/h against 150 m of head at 64 rpm and takes about 58 kW. The sump should hold at least four hours of inflow. If drainage stops, the lowest workings flood within a few hours.

7. The longwall

A longwall is a long face along the seam. A shearer travels along it and cuts the coal in strips while powered supports hold up the roof. Behind the supports the roof is left to cave in.

1. The shearer cuts a stretch of the face. About 220 kW at 64 rpm, feed up to 6 m/min. It never skips uncut coal. Lay a Create belt along the face for the coal.
2. Behind it, supports are lowered one at a time with a redstone signal or the manual lever, pushed 1 block forward with a Create piston, and set again.
3. Behind the advanced supports the roof caves. That's the goaf, and nobody goes in there.

Put water tanks on the contraption: the drum sprays leave five times less dust. A longwall exposes dozens of coal blocks a minute, and each one gives off methane. It needs plenty of air, but no faster than 4 m/s. The lower–advance–set cycle is easy to build with redstone timers, and later eras hand it to a controller.

8. Coal preparation

• Coal Jig
• Washed Coal

Run-of-mine coal carries rock, intergrowths and pyrite. The Coal Jig separates it by density: water pulses through a screen, heavy pieces settle faster, and the bed sorts into layers. It runs on a Create shaft from the left: 10 kg/s at 64 rpm, about 15 kW. It needs 0.5 l of water per kg of coal (tank 2000 l).

A Create wrench sets the clean-coal cut density: 1.40, 1.50, 1.60 or 1.70 g/cm³. A lower cut gives cleaner coal but less of it. Pyritic sulphur leaves with the heavy fraction, while organic sulphur stays in the coal.

9. Foundry and machine shop

Pump and valve bodies, flywheels and gear blanks aren't crafted. They're cast in sand moulds and finished by machining.

• Cupola Furnace
• Crucible Furnace
• Moulding Machine
• Sand Mould
• Shakeout Grate
• Lathe
• Drill Press

1. Melt. The Cupola Furnace melts grey iron from pig iron or iron ingots with charcoal (in place of coke for now), blown by a fan on a Create shaft. Fuel at 12 % of the metal gives about 1450 °C, and 10 % gives cold iron at 1345 °C. The Crucible Furnace handles copper, bronze and aluminium, one alloy at a time.
2. Prepare the mould. Right-clicking with a Casting Pattern cycles through the parts: valve body, pump casing, impeller, gear blank, wheel, flywheel, ingot mould and bearing housing. Sneak-click toggles the riser. The Moulding Machine rams foundry sand around the pattern and makes one sand mould per cycle.
3. Pour. Each furnace taps by itself into a ready mould beside it. A redstone signal keeps the tap hole closed.
4. Wait for it to solidify. Time grows with the square of the modulus, volume over surface (Chvorinov's rule). The riser's modulus must be at least 1.2 times the casting's.
5. Knock out cooled moulds on the Shakeout Grate. You get the casting back plus 90 % of the sand.
6. Machine it on the Lathe and the Drill Press with a Cutting Tool in the tool slot.

The machinist's rule. Tool life falls as the eighth power of cutting speed (Taylor). Double the speed and the tool lasts 256 times less. Pick a gear that keeps the spindle at a moderate speed.

I0 checklist

• The boiler holds pressure on a thin bed with no black smoke, and the engine turns the shaft with a dashpot fitted.
• A spare fusible plug sits by the boiler, and the procedure is on a lectern.
• The mine fan runs non-stop, the doors are closed, and the canary is alive.
• Headings are supported and stone-dusted, with barriers between the faces and the rest of the mine.
• The hoist runs within its safety factor, and the sump holds four hours of inflow.
• The jig makes washed coal, and the foundry casts pump and valve bodies with no cavities.
• You know where the deep coking-coal seams are. That's your ticket to I1.

I1–I4: what comes next

None of this is in the game yet. It's how the next eras are designed to work, and details and numbers will change. The images are placeholder models from the repository.

Reactor tiers

The core has no idea what reactor "types" are. It computes the physics from the lattice you build: fuel, moderator, coolant and absorbers. A "T2a" is simply what you get when you build an enriched UO₂ lattice in pressurized light water.

Automation ladder

The mod has no ready-made reactor controller. It gives you sensors, function blocks and peripherals, and the control system is yours to design. It grows with the plant.

1. A0
   Hands and eyes.

   Valves, levers, the pressure gauge and the gauge glass. In I0 you're the controller. The flyball governor is the only automatic device.

2. A1
   Relay logic.

   Relays, contacts and timers as blocks in the world. For example, an interlock that trips a pump when the level is low.

3. A2
   Analog computers.

   Summers, integrators and controllers. A PI controller without a computer, integrator drift included.

4. A3
   PLC and safety systems.

   Programs in LD, FBD, SFC and ST, and a cause-and-effect matrix for safety logic.

5. A4
   DCS and SCADA.

   CC: Tweaked computers, telemetry, trends and a historian.

6. A5
   Plant level.

   Planning and optimization, with Create logistics driven by Lua.