FIELD OF THE INVENTION
This invention relates to an organo-refining process to produce low ash clean coal from high ash coals for metallurgical applications.

BACKGROUND OF THE INVENTION

Organo-refining or, solvent-refining, or, solvent extraction of coal is a well established technology. However, the primary objective in most of these cases is to provide a process to produce ultra clean coal or super clean coal with ash contents less than 4%. The ash content of this parent coal (Run of Mine) is 25%.
The process for the beneficiation of coal being used currently, employs chemical beneficiation by dissolving organic matter of coal in various organic solvents. As coal is heterogeneous mixture of organic and inorganic constituents, solvolysis of coal varies with its constituents, maturity, and structural characteristics. Main advantages of this process are i) ease of recovery of solvent in the main process stream, ii) solvolytic efficiency of recovered solvents as that of fresh solvent, iii) 95-98% recovery of the solvent, iv) improved coking properties of clean coal, and v) availability of industrial organic solvents. However, the operating cost of this process is high because of high cost of solvents and energy requirement in the process.
Therefore, the need exists to develop a process for the extraction of 50% of parent coal, to obtain coal having almost 4% ash, and maintain process economy at the same time.
OBJECTS OF THE INVENTION
It is therefore an objective of this invention to propose an organo-refining
process to produce low ash clean coal, which is economical.
It is a further objective of this invention to propose an organo-refining process to
produce low ash clean coal, which uses simple means and equipment.
Another objective of this invention is to propose an organo-refining process to
produce low ash clean coal, which minimizes the heat requirement.
These and other objects and advantages of the invention will be apparent from the ensuing description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Fig. 1 : Layout of the bench scale operation according to the invention.
DESCRIPTION OF THE INVENTION
Thus, according to this invention is provided a process for the production of low
ash clean coal from high ash coal for metallurgical applications.
In accordance with this invention, coal, solvent and co-solvent are mixed
thoroughly to produce coal slurry. The coal slurry is extracted with a
predetermined ratio of coal-solvent mixture, in Section 1 of Fig. 1 in extraction
unit a sufficient high temperature is maintained to facilitate the extraction at high
temperature. A high pressure is required to elevate the boiling point of the liquid.
The temperature and pressure range is from 200°C to 300°C and 1.5 atm. to 5
atm. respectively. Due to thermal impact, the coal structure is relaxed and
extraction process is enhanced. The extraction process is continued for up to 1
hour. After extraction all the material inside the reactor is transferred to the
Filtration unit (Section 2 in Fig 1). After filtration of coal extract, the filtrate is
stored for evaporation and the residue, contains high ash percentage, partly
stored for other use and rest is recycled with feed. The filtrate is then passed to
evaporation (Section 3 in Fig 1) for concentrating the extract and the solvent
recovery from evaporator is around 70%. From top of the evaporator, the solvent vapor is collected and passed through a heat exchanger for releasing the latent heat. The liquid solvent coming from the cooler still contains sufficient
amount of heat which is collected by another cooler. Actually, hot solvent vapor
is passed through a series of two coolers for reaching a desired temperature
level.
The air is again used here for cooling medium and the hot air coming from heat
exchangers is sent to the drying unit. The concentrated material from the bottom
of the evaporator is directly discharged into the pool of water where coal is
precipitating out (Section 4 in Fig 1). Water acts here as an anti solvent and it
takes up the organic solvent. Coal does not dissolve in water whereas organic
solvent does. This property is useful for separating coal from organic solvent and
so with the addition of water, precipitation of coal occurs. After filtering out the
whole material, super clean coal is collected as residue. This super clean coal is
the final product and it contains around 4% ash. The filtrate contains organic
water mixture and it needs to be separated. The crucial part of the process is to
recover solvent from water solvent mixture.
A distillation column is incorporated here, for separating the organic solvent from
water. Distillation would make it a highly energy intensive process and drive the process towards the critical zone from where it is difficult to get economic
operation. This problem is solved by the process according to this invention,
wherein the distillation concept is replaced and solid-liquid extraction (Section 5
in Fig. 1) has been introduced. This improvement is based on the fact that coal
has greater affinity towards organic solvent, than towards water. The method
employs the step of taking out NMP by introducing raw coal.
Another useful extension of the invention is the recovery of organic solvent
(NMP) by extracting NMP by aliphatic straight chain alcohol from water NMP
mixture. According to the innovative concept NMP-water mixer is first treated
with aliphatic straight chain alcohol (Section 5 in Fig. 1). During treatment NMP
is forced to come into the organic phase and the dual layer of water organic
phase is formed from which supernatant is taking out.
The liquid-liquid layer or Solid-liquid Layer is then separated in section 6. The
organic-organic layer is then sent to the distillation unit for purifying and reuse
section 7. The clean & residue coal is then washed with water for obtaining clean
product & residue (section 8).
Therefore, organic solvent-water mixture is mixed with the feed coal and heated
for some specified time in a vessel. Due to the strong coal organic interaction, all the organic solvent is consumed by the coal. After filtration, filtrate contains
almost pure water and the residue contains coal with absorbed organic solvent
which is blended further with the portion of feed coal. In this manner, almost
pure water is obtained without distillation.
By the method according to the invention, recovery of solvent increases without
using any distillation unit which improves the techno-economics remarkably;
again part of the feed coal is getting pretreated by this process. Further, as
distillation is avoided, large amount of energy is saved. Also, the entire unit is
easy to maintain and operate.
The invention will now be explained in greater detail with the help of the
following non-limiting example.
EXAMPLE:
A 10 weight percentage solution of NMP and water mixture is prepared. A
portion of feed coal (the coal which is used as a fed material of Organo Refining
Process) having approximate solution to coal ratio of 20:1 are mixed. The
mixture is then heated for 10 minutes around 100°C and then filtered by ordinary filter paper. In warm condition coal absorbs NMP part of the mixture.
After filtration the NMP absorbed coal is collected as residue from the top of the
filter paper. The collected coal is observed to be swallowed a bit which supports
the fact that a major portion of NMP is being absorbed by coal. The filtrate is
clear liquid which is most likely to be free from organic solvent (NMP). The
filtrate and the original solution (NMP water mixture) are then titrated by
standard N/50 Nitric acid. The results of titrations are as follows.
Table 1. Titration of NMP-water mixture and NMP-water mixture after coal
treatment against with standard (N/50) HN03 as follows
Titrant Titrate value in ml Strength
1. NMP-Water mixture 4.7 0.01 (N)
2.NMP-Water mixture 0.7 0.001 (N)
after coal treatment
From the above results, it can be concluded that coal consumes appreciable
amount of NMP from the NMP water mixture. This proves the novelty of the
approach for separation of NMP from coal.

WE CLAIM:

1. A process for the production of low ash clean coal from high ash coal for
metallurgical applications, said process comprising the steps of:
coal, solvent and co-solvent are mixed thoroughly to produce a coal slurry,
extracting the coal slurry with a coat solvent mixture to obtain a coal extract,
followed by cooling the extract and filtration to obtain a residue and a filtrate,
evaporating the solvent in the filtrate and discharging the concentrated material
into a pool of water to precipitate the coal for metallurgical applications.
2. The process as claimed in claim 1, wherein the extraction is conducted at a
temperature in the range of 200 to 300°C.
3.The process as claimed in claim 1, wherein the extraction is conducted at a
pressure in the range of 1.5 atm to 5 atm.
4.The process as claimed in claim 1, wherein the extraction is conducted for upto
an hour.
5.The process as claimed in claim 1, wherein the coal extract is cooled to around
6. The process as claimed in claim 1, wherein the solvent recovered by
evaporation is 70%.
7. The process as claimed in claim 1, for producing clear coal of desired ash level
of 0.1 to 10%.