new efficient and simplified coal preparation process eng un-1

8/13/2019 New Efficient and Simplified Coal Preparation Process Eng Un-1

1/10

1

NEW EFFICIENT AND SIMPLIFIED COAL PREPARATION PROCESS

Shuyan Zhao

Tangshan Guohua Technology Co., Ltd.

Tangshan, Hebei, China

ABSTRACT:New efficient and simplified heavy medium coal preparation and slurry treatment processes,

developed by Tangshan Guohua Technology Co., Ltd., are introduced and discussed in the paper. These new

processes have become mainstream technologies in Chinese coal preparation plants and significantly

influenced Chinese coal preparation industry.

INTRODUCTION

In 21 century, heavy medium coal preparation technologies have been developed rapidly in China. The

coal preparation capacity using heavy medium processes surpassed that using jigging process first time in

China in 2007. This resulted from a series of heavy medium process technologies developed by Chinese coal

preparation researchers since 1980s, especially from many new efficient and simplified coal process

technologies developed by Tangshan Guohua Technology Co., Ltd. in last 10 years, which played a

significant important role in the such development.

The new coal preparation processes, developed by Tangshan Guohua Technology Co., Ltd., have been

recognized rapidly by Chinese coal preparation industry due to their high efficiency, simplification, energy

saving, and discharge reduction. Since 2000, Tangshan Guohua Technology has designed and contracted more

than 330 heavy medium coal preparation plants, in which the production capacity of the largest plant was

2362 st/h. The coal preparation plant engineering projects, designed by Tangshan Guohua Technology Co.,

Ltd. during 2008 - 2009, covered close to 70% of the coking coal market in China.

HEAVY MEDIUM COAL PREPARATION PROCESS WITHOUT DESLIMING & SIZING OF RAW

COAL FEED

Sizing and desliming of raw coal feed is the conventional heavy medium coal preparation process, in

which the raw coal is classified first. Large size lump coal is processed with heavy medium vessel or the other

heavy medium separators. Small size coal after deslimed is processed using a single or two stages of H.M.

cyclones with a single or double (high and low) densities of heavy media. Coarse fine coal is processed with

spiral, TBS, or the other separators. This traditional heavy medium process is not only complicated but also

produces low separation efficiency for the coarse fine coal. Even no qualified clean coal can be produced

when difficult washing coal is processed. In addition, larger size of low separation limit results in a large


2/10

2

amount of fine coal entering the relative high cost and low efficient flotation operation.

Using the developed new heavy medium process without desliming & sizing, three qualified products

including clean coal, middling and reject or two products (clean coal and reject) can produced at one time

using a single low density heavy medium suspension instead of using high density or double densities of

heavy media. The new heavy medium process not only considerably simplifies process flow circuits but also

significantly improves separation efficiency. In addition, the new process solves the problem with which pure

reject cannot be produced at high density (1.9 kg/L) for Chinese coal using heavy medium vessels or the

other H.M. separators or 2-product cyclones.

Process Features of the Heavy Medium Cyclone

Since the velocity gradient in the H.M. cyclone destroys the structure viscosity of heavy medium

suspension, the separation efficiency of non-deslimed coal is still very high if the structure dimensions of the

cyclone and operating parameters are set up properly. Table 1 shows the separation results using 3-product

cyclones without desliming & sizing of different washability raw coals from four Chinese coal preparation

plants.

Table 1. Separation results using 3-product H.M. cyclones

The data in Table 1 indicate the high separation efficiencies were obtained in all the four coal plants for

the different washability coals; Probable error Epm1=0.020-0.025kg/L (1ststage), Epm2=0.040-0.050kg/L (2nd

stage), and recovery>97% are achieved and reach or surpass the separation efficiencies of the other plants

using the other H.M. processes.

Low Separation Limit and Fine Coal H.M. Cyclone

The low separation limit, using 3-product H.M. cyclone without desliming & sizing, is what every

process technician and engineer would like to know. The plant tests of 60gravity-fed 3-product cyclone,

developed by Tangshan Guohua Technology Co., Ltd., were carried out in Shenhua Mengxi Qipanjing Coal

Plant

Feed

Size

inch

0.1

Amt

%

Ash, % Clean yield

%

Separation Density

kg/L

Probable Error Epm

kg/LRecovery

%Raw Clean Middling Reject 1ststage 2ndstage 1ststage 2ndstage

Shanxi Wenfeng 3 1/8-0 6.55 15.77 6.37 35.23 80.27 82.04 1.529 1.963 0.022 0.048 98.9

Anhui Linhuan 3 3/4-0 14.30 36.03 9.79 37.79 85.17 61.79 1.540 1.860 0.020 0.040 99.5

Guizhou Laowuji 3 1/8-0 38.26 34.22 9.54 24.47 76.99 56.65 1.430 1.688 0.025 0.045 99.8

Shanxi Jinyan 3 1/8-0 47.58 31.78 11.51 27.89 67.66 49.95 1.476 1.749 0.021 0.042 97.4


3/10

3

Preparation Plant in April 2009. The separation probable error Epm=0.099kg/L for the fraction of 0.5-0.25

mm (32-60 mesh) was obtained at the raw coal throughput of 648-668 st/h. The test results and partition

curve for 0.5-0.25 mm (32-60 mesh) fraction are shown in Table 2 and Figure 1.

Table 2. Test results of 0.5-0.25 mm size fraction in Qipanjing Coal Preparation Plant

Density

kg/L

Raw coal Clean coal Middling Reject Calculated Raw Clean

partition

%

In fraction

%

Ash

%

In fractn

%

In total

%

Ash

%

In fractn

%

In total

%

Ash

%

In fractn

%

In total

%

Ash

%

In fraction

%

Ash

%

1.80 12.32 71.62 0.77 0.58 67.10 44.31 9.82 63.00 86.12 2.07 74.81 12.47 65.15 95.34

Total 100.00 20.09 100.00 75.44 11.24 100.00 22.16 41.20 100.00 2.40 69.27 100.00 19.27

%

Figure 1. 0.5-0.25 mm fraction partition curve

Based on the Chinese coal industrial test standard MT/T811, the size at which its separation probable

error Epm0.1 kg/L is considered as the low separation limit of the equipment at coal size0.5 mm (32

mesh). Therefore, the low separation limit of the 60 gravity-fed 3-product H.M cyclone developed by


4/10

4

Guohua has reached 0.25 mm (60 mesh).

The low separation limits of H.M. cyclone processes in many coal preparation plants, designed by

Tangshan Guohua, have reached 0.25 mm (60 mesh) in China. For extreme difficult washing coal or required

lower separation limit than 0.25 mm (60 mesh), the fine coal H.M. cyclones, developed and patented by

Tangshan Guohua, can be utilized to further reduce the low separation limit. The working principle for the

fine coal H.M. cyclone is that the magnetite carried with clean coal is always finer due to the effect of

centrifugal force on the magnetite particles in the cyclone. The finer fraction of H.M. suspension drained

from the clean coal can be used as the separation H.M. suspension for the fine coal H.M. cyclone. Therefore,

no special ultrafine magnetite suspension is required to make, transport, and recover, which significantly

simplifies the H.M. process flow circuit.

The low separation limit of the fine coal H.M. cyclone can reach 0.1 mm (150 mesh). The detailed

process flow circuit is shown in Figure 2. The separation results are given in Table 3.

Figure 2. The process flow circuit using the fine coal H.M. cyclone


5/10

5

Table 3. Separation results using the fine coal H.M. cyclone in Xinzhuangzi Coal Preparation Plant in Anhui China

Separation

density, kg/L

Probable error

Epm, kg/L

Feed, % Celan coal, % Middling, %

Yield Ash Yield Ash Yield Ash

1.52 0.08 100.00 20.33 67.56 9.69 32.44 42.50

Heavy Medium Consumption

The heavy medium consumption, using the H.M. cyclone without desliming & sizing, is also what the

every coal process technician and engineer would like to take care of. Low heavy medium consumption is

able to be realized based on our industrial practice if we make sure to do the follows:

- Proper selection of magnetic separator and good operation adjustment- Proper selection of drain and rinse screen. Screen width, screen deck structure, and spray position are

all important

- There should be enough circulated H.M. suspension slit out to avoid too high viscosity- Make sure to have clear thickener overflow to realize using clear water to rinse the materials on the

H.M. drain screen deck

Tangshan Guohua designed many heavy medium process plants without desliming & sizing of raw coals

in China. The average H.M. consumption, using 3-product cyclone without desliming & sizing, is 1 kg/t.

The heavy medium consumptions in some of plants are very low. For example, H.M. consumption in

Wenfeng Coal Preparation Plant of Shanxi China was as low as 0.55 kg/t in 2006 and has been kept

consistently. Industrial practice indicates the H.M. consumption using non-desliming and non-sizing of raw

coal is close to that using pre-desliming and sizing of raw coal.

CLEAN FINE COAL SLURRY FLOW CIRCUIT

The fine coal slurry circuit in a coking coal preparation plant can be divided into two parts, i.e., clean

fine coal flow circuit and fine tailing flow circuit.

Purposes of the clean fine coal treatment circuit are:

- Economically and efficiently separate the fine coal fraction- Reduce the moisture content of clean fine coal as much as possible.

The clean fine coal process circuit with two stage flotation and two stage dewatering & recovery,

promoted by Tangshan Guohua, is shown in Figure 3. The tailing of clean coal magnetic separator is pumped

to clean fine coal sieve bend to classify. The underflow of the sieve bend enters the 1st stage flotation while


6/10

6

the overflow of the sieve bend, combined with the froth of the flotation, is dewatered and recovered with a

screen-bowl centrifuge to primarily recover >0.045 mm (325 mesh) fraction of coarse fine coal.

The fine fraction of


7/10

7

Unique classified flotation process technologyFloatability and selectivity of most Chinese fine coals are difficult since a large amount of high

ash clay is usually contained in the flotation feed of


8/10

8

Pressurized filters and clean coal filter presses are employed in many cases to dewater and recover the

fine clean coal in one stage in some of coal plants in China. However, construction capital cost could be

reduced by 14.3% and manpower saved by 37.5% using our promoted 2+2fine circuit compared to using

the one stage of filter press. Electrical power consumption could be reduced by 70.45% and construction

capital cost saved by 54.05% using our promoted 2+2 fine circuit compared to using the one stage of

pressurized filter.

TAILING SLURRY TREATMENT FLOW CIRCUIT

The purpose of fine tailing treatment flow circuit promoted by Tangshan Guohua is described as below:

Recover coarse fine reject as much as possible to reduce its moisture content and to mix it into themiddling product to increase its value

Realize complete separation of solid and liquid for the small amount fine tailings Addition of Ca++ and Mg++ ionic type agglomerates as a primary agent and polypropylene type

flocculant as a secondary agent to ensure the overflow of thickener clear to realize using clear water

to wash coal.

Figure 4. Tailing treatment process flow circuit with 2-stage thickening and 2-stage recovery

The tailing treatment process circuit flow diagram with 2-stage thickening and 2-stage recovery is shown

in Figure 4. Tailings (flotation tailing and tailings from the reject and middling magnetic separators after

coarse fines removed) first enter the 1ststage incline tube thickener to classify. The underflow of the thickener


9/10

9

is dewatered with a screen-bowl centrifuge to primarily recover >0.045 mm (325 mesh) coarse fine fraction.

The overflow of the thickener enters the 2nd stage incline tube thickener. The underflow of the 2 nd stage

thickener is dewatered using a filter press to completely recover all ultrafine tailings. The clear overflow of

the 2ndstage thickener and clear filtrate of the filter press are used as wash water circulated in the plant to

realize using clear water to wash coal.

Currently one stage of filter press is widely used to recover the fine tailings in the world. Sometimes,

the tailings are also discharged to tailing ponds or tailing dams in some of plants. The low heating value

tailing coal is abandoned. The disadvantages using one-stage filter press are 1) sticky filter cake brings

troubles to material sales on the market, 2) multiple units of filter presses have to be used due to low

production capacity of the filter press, which results in high construction capital cost, and 3) ultrafine tailings

are accumulated and a vicious circle takes place if the coal contains a large amount primary slime and

ultrafine clay materials. The tailing ponds or tailing dams are prohibited in China due to the strict

environment regulations

Table 5Process parameters of LWZ series screen-bowl centrifuge

Coal plant Aiweiergou Plant, China Huoshaopu Plant, China Wangfenggang Plant, China

Applications Clean coarse fine dewatering Tailing coarse fine dewatering Tailing coarse fine dewatering

Date of tests 2006.7 2003.11 2008.3

Feed

Solid

content

g/L 278.5 470 253.6

% 25.64 39.38 22.96

Ash, % 11.42 40.12 48.63

Dewatered

products

Surface moisture, % 15.24 15.70 12.50

Ash, % 11.10 36.54 45.72

Yield, % 78.81 70.54 81.06

Solid recovery, % 86.91 70.54 81.06

Liquid mixing rate, % 5.39 8.53 3.45

Screen-bowl

filtrate

Solid

content

g/L 54.20 187.00 56.50

% 5.33 10.61 5.52

Ash, % 12.28 48.68 53.01

Yield, % 11.87 29.46 18.94

Screen-bowl

overflow

Solid

content

g/L 132.40

% 12.72

Ash, % 15.88

Yield, % 9.31

Dewatering efficient, % 81.52 62.01 77.61


10/10

10

The LWZ series of screen-bowl centrifuges with centrifugal force 200-280 and length/diameter ratio

1.43-2.00 is recommended to use in the 2+2model tailings treatment circuit promoted by Tangshan Guohua

to primarily recover >0.045 mm (325 mesh) coarse fine tailings. The recovery rate of >0.045 mm (325 mesh)

fraction is more than 97%. Removing rate of

new efficient and simplified coal preparation process eng un-1

Documents