The Morbi manual gives slurry moisture going into the spray dryer as 35 to 40% in one place and 33 to 35% in another: which is right, and what does it cost in water to remove?

The Morbi manual prints 35 to 40% water in the slurry going into the spray dryer in one section and 33 to 35% in another, both drying to 5 to 6%. Taking out the extra water means evaporating about 40% more per tonne of powder at 40% than at 33%.

What a spray dryer does, in plain words

Tile clay is ground with water into a thin slurry. The spray dryer sprays that slurry into a hot chamber, the water leaves as steam, and a dry powder falls out for the press. The fuel burnt there is mostly spent turning that water into steam. So the more water in the slurry, the more fuel for each tonne of powder.

The two figures

• Section 2.3.1, the process description: input moisture to the spray dryer is 35 to 40%, dried to 5 to 6%.
• Section 3.3.1, the technology review: slurry holds moisture of around 33% to 35% on a weight basis, dried to powder at 5% to 6%.
• The polishing project report from the same study gives 35 to 40% going down to 5 to 6%, matching the first.
• The ranges overlap only at 35%. The manual does not say why they differ, or which units each describes. They may be different samples of units, which is my guess.

What the water costs

Take one tonne of powder at 5% moisture, which holds 950 kilograms of dry clay. If the slurry is 33% water, it weighs 950 / 0.67 = 1,418 kilograms, so about 418 kilograms of water has to leave. At 35% it is 1,462 kilograms and 462 kilograms of water. At 40% it is 1,583 kilograms and 583 kilograms.

The step from 33% to 40% water adds 583 / 418 = 1.40 times the water to evaporate. This sum takes the moisture as a share of the wet weight, which the 3.3.1 wording says; the 2.3.1 wording does not say.

What the manual says about water in the mill

Its housekeeping list says water added to the ball mill or blunger through a drum or bucket can raise spray dryer energy use by 1% to 3% if too much is added, and that the moisture of the powder leaving the spray dryer should be watched regularly. Its best-practice list also suggests a water monitoring system on the ball mill or blunger to cut spray dryer fuel.

What to log

• Slurry moisture from the lab, at least once a shift (my advice, not the manual's).
• Powder moisture from the silo.
• Tonnes of powder made, and spray dryer fuel for the same hours.
• Fuel for each tonne of powder, monthly, beside the slurry moisture average. If one rises with the other, the water is where the fuel goes.

Water to evaporate for one tonne of powder

• Dry clay in one tonne of powder at 5% moisture: 1,000 x 0.95 = 950 kg
• Slurry at 33% water: 950 / 0.67 = 1,418 kg, so 418 kg of water leaves
• Slurry at 35% water: 950 / 0.65 = 1,462 kg, so 462 kg leaves
• Slurry at 40% water: 950 / 0.60 = 1,583 kg, so 583 kg leaves
• 40% against 33%: 583 / 418 = 1.40

The arithmetic is exact for the moisture figures the manual gives. It tells you water to remove, not fuel burnt, which depends on your dryer.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so a unit's own gas, oil and power lines are on file to set beside the report's figures. It does not measure a kiln or replace an audit.

• Spray dryer fuel and carbon dioxide per tonne of powder
• Morbi cluster energy and carbon
• Morbi gas and power per square metre

Sources: BEE, Manual on Energy Conservation Measures in Ceramic Industry, Morbi cluster (SAMEEEKSHA), BEE, Detailed project report: energy conservation in polishing section, Morbi (SAMEEEKSHA)

Last reviewed 2026-11-07. Moisture figures are from the April 2010 Bureau of Energy Efficiency (BEE) Morbi manual (sections 2.3.1, 3.2.4 and 3.3.1) and the polishing project report. They describe 2009 to 2010 practice.