Application case 11: The alumina production process and related solutions

一.Process

The whole process of alumina production process is divided into 7 workshops, each workshop completed one or several processing function.

1. The first workshop: crushing ore and bauxite homogenization

1.     The second workshop: generation of raw slurry and raw material formula

1)      Raw slurry

2)      Raw material formula

2.     The third workshop: Firing workshop

1) raw slurry from the second workshop, workshop after the slurry tank on the rotary sieve in stone, carbon block and other debris enters into the slurry tank, the oil isolation pump pressure, sprayed into the kiln by a spray gun, the raw meal after through the drying zone becomes dry raw material, following rotary belts of rotary kiln, gradually moves to the end - kiln head, respectively through preheating zone, decomposing zone, and firing zone, complete the sintering reaction and then get into the cooling zone, the clinker cooling machine cooling, is sent to a crusher, the trough conveyor, zipper machine into the clinker silo storage backup.

2) Sintering clinker kiln is done at high temperature, heat and combustion of pulverized coal clinker sintering production. Therefore the workshop equipped with pulverized coal preparation system: a workshop to coal belt conveyor in the coal bunker, the electromagnetic vibration feeder into the coal grinding, grinding, and then the coarse powder, fine powder, bag type dust collector, the rotary feeder into the coal used for firing.

Due to the adoption of injection feeding and high temperature sintering, carrying a large number of dry raw materials and volatiles in the smoke in the exhaust (i.e. clinker kiln dust), and their number is equivalent to about 65-110% clinker production, therefore the workshop with the vertical flue, cyclone dust collector, electric precipitator and the spiral conveyor, hoist, chimney facilities of dust and ash into the kiln.

3.      The forth workshop: wash the red mud and stripping

Use the separation process with the low load coefficient (1.16~1.20), low concentration of sodium carbonate (22~27g/l), stripping through a closed wet grinding, adding flocculant to sediment red mud. The clinker workshop sent, by measuring plate machine into the leaching mill, join the red mud lotion, carbon denominator liquid and white mud lotion after gate flow meter and clinker according to a certain proportion into the leaching mill crushing leaching, size grading grinding slurry and classifier in coarse sand, return to ground, the classifier overflow (extract) send separation tank, adding flocculant solution was separated, the isolated liquid (coarse liquid) send to the desilication workshop for desilication. The red mud separation after the washing step heating water supply, and add the flocculant 7 reverse washing. The red mud washing after sent to the red mud dam yard. The red mud yard returns back into the heat sink in.

4.     The fifth workshop: desilication

Main task: A. After heating the crude liquid post from four workshops, adding sodium silicon slag and spent liquor, then coarse groove to the desilication. A part of the solution for pressure cooking desilication in the conditions of high temperature, high pressure desilication; a part of normal pressure desilication solution.

B. pressure digestion solution desilication of sodium silicon slag separation, the overflow into synthetic liquid were three deep desilication after calcium silica slag separation, the index of silicon solution (A/S) reached more than 600. Normal pressure desilication solution with synthetic liquid and reaction trough reaction, the index of silicon solution (A/S) reached more than 300.

C. solution through the filter, filter and silicon slag separation to obtain qualified refined sodium chlorate solution (semen), according to needs to six workshop decomposition (carbonation and seed precipitation); silicon slag according to need to return the crude tank as the crystal seed or send two workshop configuration meal oar.

D. usesthe exhaust gas of buffer tank to heat the circulating water and the return water of dam, and then sent to the fourth workshop with the condensation water of the casing preheater.

5.     The sixth workshop: evaporation, kind of, carbon

The sixth workshop in alumina production plays the decomposition of sodium aluminate solution, aluminium hydroxide separation and washing and mother liquor evaporation, and the aluminium hydroxide solution qualified send stripping; qualified carbon evaporation mother liquor to silicon slag separation and two workshop for evaporation mother liquor ingredients, will send desilication, will be eligible to return to the boiler room and varieties of workshop task, two times of washing.

1.       The Seventh workshop: qualified alumina baking workshop

Task: The sixth workshop send slurry by pan filter, get the qualified Al (OH) 3, the aluminium hydroxide filter table or drum filter by calcination of alumina feeding into qualified warehouse storage.

2.        Control system configuration

Nanshan Donghai alumina control system I/O points summary

Zhongzhou branch of China Aluminium Company Bayer mineral processing method of baking I/O point configuration

	Automatic control professional
	AI(4-20mA)	AO(4-20mA)	DI(24VDC)	DO(24VDC)	RTD	SI(MODBUS RTU RS485)
Aluminium hydroxide baking Aluminium hydroxide filter	124	48	416	128	0	1
Total	240	48	416	128		1

Figure: alumina baking process