A Solvay plant needs six pieces of equipment: a brine tank, an ammonia tower that saturates brine, a cooled carbonation tower, a filter for the bicarbonate crystals, a kiln that heats bicarbonate to soda ash at about 200 °C, and a lime kiln above 900 °C that supplies carbon dioxide and quicklime. Size it from the daily tonnage: one tonne of soda ash a day needs at least 1.1 tonnes of salt, which is about 3.5 cubic metres of saturated brine. Ammonia attacks copper and zinc alloys, so build the ammonia circuit from steel.
Part of Industrial Chemistry
The vessels, towers, kilns and filters of ammonia-soda manufacture, with the sizing arithmetic and the materials choices.
Six Pieces, Each With A Job
The carrier’s equipment table:
| Component | Purpose | Construction |
|---|---|---|
| Brine tank | Dissolve salt | Stone, wood or lined steel |
| Ammonia tower | Saturate brine with ammonia | Tall steel column with packing |
| Carbonation tower | React ammoniated brine with CO2 | Tall steel column, cooled |
| Filter | Separate sodium bicarbonate crystals | Cloth filter, press |
| Kiln | Convert bicarbonate to soda ash, at 200 °C | Brick or steel |
| Lime kiln | Produce CO2 and quicklime, 900 °C and above | Brick kiln |
Why a tower: a tall column with packing forces gas and liquid to meet over a large surface as the liquid trickles down against the rising gas. The cooling of the carbonation tower follows from the carrier’s rule of keeping it cool, and the chemistry is in Solvay Chemistry.
Materials: Where Each Choice Comes From
- Ammonia and brine. Mild steel is listed in the carrier’s vessel table as good for ammonia and general reactions; ammonia attacks copper and zinc alloys (brass), a general fact, so keep brass fittings out of the ammonia circuit.
- Wet bicarbonate and chloride liquors. Chloride corrodes ordinary steel over time. Stone, stoneware or glass-lined parts and sacrificial thickness are the cures; see Reaction Vessels and Chemical Vessels.
- The lime kiln. See Lime Kiln for a draw-kiln design.
- Heat exchange. Cooling the carbonation tower uses coils or jackets; see Heat Exchangers.
What You Need
- Brine supply and storage, with salt sources from Salt Production and Sourcing.
- Piping, valves and seals compatible with ammonia and hot chloride liquor, with gaskets as in Gaskets and Seals.
- Pumps or gravity feed, cooling water and a gas blower.
- Waste handling for calcium chloride liquor.
Method: Sizing From The Daily Target
Step 1: Fix the daily soda-ash tonnage.
Step 2: Compute salt from the reaction masses, then brine volume from the carrier’s saturated brine strength.
Step 3: Compute limestone to give the kiln its CO2 and lime.
Step 4: Size towers and filters from the flows and pilot-scale behaviour. This corpus does not provide tower dimensions, and none are invented here.
Worked Example: One Tonne Per Day
The overall reaction is 2NaCl + CaCO3 → Na2CO3 + CaCl2.
- Theoretical salt: 1,000 kg × 117 ÷ 106 = 1,104 kg, so at least 1.1 tonnes of salt per tonne of soda ash (real yield is below 100%).
- Saturated brine is about 26% salt by weight (the carrier’s figure). Brine mass: 1,104 ÷ 0.26 = 4,246 kg.
- Brine density about 1.2 kg per litre (a recalled value). Volume: 4,246 ÷ 1.2 = 3,540 litres, or 3.5 cubic metres.
- Limestone for the kiln: 1,000 × 100 ÷ 106 = 943 kg.
A real plant at under 100% yield uses more of each, and the brine tank should hold at least one day’s volume. The waste calcium chloride is 1,000 × 111 ÷ 106 = 1,047 kg per day, which needs somewhere to go.
Common Mistakes
- Using brass or copper fittings on the ammonia side.
- Building the carbonation tower without cooling.
- Skipping filter spares: cloth tears and blinds.
- Leaving the lime kiln out of the plan.
Safety
Tall towers, hot kilns and toxic gas
Ammonia leaks are toxic and corrosive; carbon dioxide from the kiln collects in pits; kilns above 900 °C burn and radiate heat. Use platforms and rails for tall towers, vent every tank to a safe outdoor place, and never enter a tank or pit while it may hold gas. See Toxic Gases and Safety and Waste.
What’s Next
- Learn next: Reaction Vessels — materials, pressure and seals in general
- Combine with: Waste Treatment — the calcium chloride stream