Title of Invention

A METHOD FOR EVAPORATING LIQUOR USED IN AN ALUMINA PRODUCTION WITH COMBINED EVAPORATORS

Abstract Combined Falling-film Evaporation Method A combined falling-film evaporation method comprising the step of employing a tube type falling-film evaporator and a plate type falling-film evaporator to evaporate the evaporation raw liquor to obtain the recycled liquor, characterized in that during the evaporation procedure, when the temperature is >100'C and alkali concentration >l90g/l, the tube type falling-film evaporator is used, and when the temperature is <100°C and alkali concentration <190g/l, the plate type falling-film evaporator is used.
Full Text

Combined Falling-film Evaporation Method
Technical Field
The present invention relates to a method of evaporating the slurry in alumina
production,
Background
During alumina production, if diaspore and boehmite are used as raw materials, evaporators are needed to evaporate the spent liquor so as to obtain the desired recycled liquor. The existing evaporation processes include five effect evaporation process or six effect evaporation process. That is, the spent liquor flows through in sequence five or six evaporators to obtain the recycle liquor, and vapor is used to heat the evaporators in turn in an opposite direction. Currently, there are the following two kinds of evaporators evaporating the spent liquor:
Tube type falling-film evaporator: a steel tube is used as a heating element; such evaporator has advantages such as adapting to high temperature and high concentration of alkali, wear resistance, easy inspection and maintenance, and a long working life. The shortcomings of said evaporator resides in heavy weight and requirement for a large investment,
Plate type falling-film evaporator: a plate sheet formed by welding from two stainless thin plates is used as a heating element. The plate type falling-film evaporator uses steel material about 40 percent less than the tube type falling-film evaporator for the same heating area. The plate type falling-film evaporator has a high heat conductive coefficient and can heat quickly. However, due to problems in plate sheet welding and plate materials, corrosion is likely to appear under a high temperature and a high caustic concentration, thus damaging the plate sheet, and furthermore, damage of one plate sheet will cause stop of operation of the whole evaporator set and lead to a

Summary of the Invention
An object of the present invention is to provide a combined falling-film evaporation
method, which combines advantages of the existing two kinds of evaporators and can
reduce the production cost.
The combined falling-film evaporation method according to the present invention is
as follows: it uses the tube type falling-film evaporator and the plate type falling-film
evaporator to obtain the recycled liquor from the evaporation of spent liquor. During
the evaporation procedure, when the temperature is >100*C and caustic concentration >190g/l, the tube type falling-film evaporator is used* and when the temperature is
Compared with the existing technology, the tube type falling-film evaporator is used under high temperature and high caustic concentration and the plate type falling-film evaporator is used for low temperature and low caustic concentration. In the present invention, drawbacks of the two evaporators are fully taken into consideration and advantages of the two kinds of evaporators arc incorporated, According to the present invention, inspection and maintenance are convenient, a long working life is exhibited and production cost is reduced.
Brief Introduction of the Drawings
Fig. 1 is a schematic view showing the process flow chart of the present invention.

Practical Implementation
Combining the existing tube type falling-film evaporator and plate type falling-film evaporator. In a six effect evaporation process, the spent liquor (A) flows into the sixth effect evaporator (6) and then into the fifth (5), the fourth (4), the third (3), the second evaporator (2), and the first effect evaporator (1) to obtain the first effect solution for the subsequent work sections; vapor (B) is heated from the first effect evaporator (1) i.e. heat the evaporators in a counter direction and finally enters the sixth effect evaporator (6)> wherein when the temperature in the first, second and third
effect evaporators is >10G°C and caustic concentration >190g/l, the tube type falling-film evaporator is used, and when the temperature in the fourth, fifth and sixth effect
evaporators is



Claims
1, A combined falling-film evaporation method comprising a tube type falling-film
evaporator and a plate type falling-film evaporator to obtain the recycled liquor from
evaporation of spent liquor, characterized by during the evaporation procedure, when
the temperature is >1000C and caustic concentration >190g/l, the tube type falling-
film evaporator is used, while the temperature is 2, The combined falling-film evaporation method described in claim 1 is
characterized by a fact that when a five effect evaporation process is adopted, the tube
type falling-film evaporator shall be used for the first and second effect evaporation
while the plate type falling-film evaporator shall be employed for the third, fourth and
fifth evaporation.
3, The combined falling-film evaporation method described in claim 1 i$ featured
with a fact that when a six effect evaporation process is adopted, the tube type falling-
film evaporator shall be applied for the first, second and third effect evaporation and
the plate type falling-film evaporator shall be used for the fourth, fifth and sixth
evaporation.


Documents:

1679-CHE-2005 AMANDED CLAIMS 29-04-2010.pdf

1679-che-2005 amanded pages of specification 29-04-2010.pdf

1679-CHE-2005 CORRESPONDENCE OTHERS 29-04-2010.pdf

1679-CHE-2005 AMANDED PAGE OF SPECIFICATION 05-11-2009.pdf

1679-CHE-2005 CLAIMS GRANTED.pdf

1679-CHE-2005 CORRESPONDENCE OTHERS.pdf

1679-CHE-2005 CORRESPONDENCE PO.pdf

1679-CHE-2005 EXAMINATION REPORT REPLY RECIEVED 05-11-2009.pdf

1679-CHE-2005 FORM 1.pdf

1679-CHE-2005 FORM 18.pdf

1679-CHE-2005 OTHER DOCUMENT 05-11-2009.pdf

1679-CHE-2005 POWER OF ATTORNEY 05-11-2009.pdf

1679-che-2005-abstract.pdf

1679-che-2005-claims.pdf

1679-che-2005-correspondnece-others.pdf

1679-che-2005-description(complete).pdf

1679-che-2005-drawings.pdf

1679-che-2005-form 1.pdf

1679-che-2005-form 3.pdf

1679-che-2005-form 5.pdf

1679-che-2005-other-documents.pdf


Patent Number 241439
Indian Patent Application Number 1679/CHE/2005
PG Journal Number 28/2010
Publication Date 09-Jul-2010
Grant Date 02-Jul-2010
Date of Filing 18-Nov-2005
Name of Patentee CHINA ALUMINIUM INTERNATIONAL ENGINEERING CORPORATION LIMITED
Applicant Address B-15/F, TONGTAI MANSION,33 JINRONG STREET, XICHENG DISTRICT, BEIJING 100032
Inventors:
# Inventor's Name Inventor's Address
1 SUN, PEILIN 208, BEIJING ROAD, GUIYANG CITY, GUIZHOU PROVINCE 550004
2 LUO, XIANQING 208, BEIJING ROAD, GUIYANG CITY, GUIZHOU PROVINCE 550004, CHINA
3 SHEN, MINGLIANG 208, BEIJING ROAD, GUIYANG CITY, GUIZHOU PROVINCE 550004, CHINA
PCT International Classification Number B01D 1/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2004101554612 2004-11-19 China