INTERIM FINAL TECHNICAL REPORT

November 1, 1998, through October 31, 1999

Project Title: DEVELOPMENT AND DEMONSTRATION OF AN ENHANCED GRAVITY SEPARATOR FOR COAL CLEANING

ICCI Project Number: 98-1/4.1B-2

Principal Investigator: R. Q. Honaker, Southern Illinois University

Other Investigators: D.P. Patil, Southern Illinois University

Project Manager: Ken Ho, ICCI

ABSTRACT

The main objective of this project was to demonstrate the ability of a Falcon Concentrator in combination with an advanced flotation system to improve the separation efficiency of fine coal cleaning over an existing conventional circuit at an operating Illinois coal preparation plant. Due to an expansion in the facilities, the in-plant commercial demonstration portion of the project has been delayed and, thus the results presented in this report were obtained from pilot-scale experimental programs.

The technical and economical evaluations of the project are based on the Jader Fuels coal processing plant, which treats Illinois No. 2 and No. 3 coals. The raw feed contained about 20% ash with the Illinois No. 2 coal seam having a total sulfur content of nearly 6.0% as compared to 4.0% for the Illinois No. 3 seam. Preliminary Falcon tests were conducted with -48 mesh Illinois No 2 coal with varying bowl speeds, feed flow rates, underflow rates and bowl angles. Using a bowl angle of 10°, it was possible to obtain a clean coal yield of 72.7% with 7.3% ash and 1.12% pyritic sulfur from a feed coal containing 20% ash and 3.46% pyritic sulfur. Utilizing a bowl angle of 14° produced a similar product quality at a significantly greater mass yield value of 81.3%. The theoretical yield at 8% ash is about 90%, which indicates that the Falcon concentrator provides an excellent separation performance.

After plant modification, coal samples from the feed to the classifying cyclones and refuse stream were collected. Under optimized conditions, the Falcon Concentrator reduced the ash content of the 1000 x 44 m refuse material from 47.23% to 8.72% with nearly 40% mass yield to the product. The corresponding reduction in total sulfur content was from 7.21% to 2.64%, which was due to an 88% rejection in pyritic sulfur. This separation is nearly perfect as indicated by an organic efficiency greater than 90%, which compares the actual versus the theoretical yield. Furthermore, the probable error (E_p) and specific gravity of separation (d₅₀) were 0.12 and 1.45, respectively. Utilizing these excellent process efficiencies, the total sulfur content in the classifying cyclone feed was decreased from 5.54% to 2.26% while recovering 86% of the combustibles and rejecting 72% of the ash-bearing material. High separation efficiency was again obtained as indicated by a 90% organic efficiency value.

EXECUTIVE SUMMARY

Enhanced gravity concentration is a product of the research conducted aimed at improving the efficiency of fine particle processing. Research funded, in a large part by the State of Illinois, has found that enhanced gravity concentration has the ability to improve the rejection of both ash-bearing material and coal pyrite while maximizing the recovery of fine coal. The process effectively treats particle sizes from 16 mesh to as small as 325 mesh. Based on successful research programs conducted on bench, pilot plant and full-scale units, the present project was funded to evaluate the application of a full-scale enhanced gravity concentrator, commercially known as the Falcon, Concentrator in an operating preparation plant. The goal of the project is to install and evaluate the Falcon Concentrator in conjunction with an advanced flotation system for the treatment of -16 mesh coal at the Jader Fuels preparation plant located in southern Illinois and quantify the resulting techno-economical benefits.

The Jader Fuels preparation plant treats approximately 400 tons/hour of coal from the Illinois No. 2 and No. 3 seams as a blended run-of-mine feed. The coarse coal is cleaned using Baum jigs, intermediate fraction with water-only cyclones and the minus16-mesh fraction with spiral concentrators. The following samples were collected from the Jader coal preparation plant for characterization in pilot plant studies:

· -1 mm feed to the classifying cyclones containing a mixture of Illinois No. 2 and 3 coals;

· Plant refuse stream material.

Samples from composite feed to the cyclone and plant refuse were collected in separate barrels. These samples were homogenized and a representative sample was taken for characterization. The samples were subjected to particle size analysis; particle size-by-size washability tests. The resulting samples were analyzed for ash, total sulfur and calorific contents.

The refuse coal contains about 45.33% ash and 5.52% total sulfur, of which, about 60% is pyritic sulfur. The classifying cyclone feed contains 30.39% ash and 3.91% total sulfur. The refuse sample contains about 27% by weight of -400-mesh having an ash content of about 49%. Whereas, the classifying cyclone feed contains about 30% of -400 mesh fraction with an ash content of 50%. Hence, removing the -400 mesh fraction from both samples improves the grade of the coal. The heat values for the refuse and composite samples are 7789 and 9647 BTU/lb, respectively.

The washability analysis data (Figure 1) obtained on a particle size fraction +16 mesh shows that at about 6.7% ash, the clean coal yield is 50%. For size fraction 16 x 28 mesh the clean coal is yield 36% at about the same ash level of 6.5%. The washability data for other fractions shows that for an ash content of about 6.5% the clean coal yield is in the range of 50 to 60%. The near gravity material within the specific gravity rage of 1.5 to 1.8 is in between 1 to 3%. This finding suggests that the particles are liberated and a moderately efficient gravity separator is sufficient to ensure a high level of combustible recovery. However, since most of the material (72%) is below 48 mesh it is essential to use an enhanced gravity technique to achieve the required combustible recovery.

Figure 1:  Particle size-by-size washability curves, which represents the theoretically best product yield achievable at any given product ash, for the corresponding feed size fraction from the treatment of the Jader refuse material.

A parametric test program was conducted to evaluate and optimize the parameter values of the Falcon Concentrator using a Box-Benkhen design. The following parameters and associated value ranges were examined in the experimental campaign:

· Bowl speed (20, 30, 40 Hz);

· Feed solids content (10, 20, 30 % by wt.)

· Underflow rate (1, 3, 6 lpm)

· Feed flow rate (10, 20, 30 gpm)

Using the Design Expert software for data interpretation, the following empirical models describing the product ash content and combustible recovery as a function of the operating parameter values were derived in quadratic form for refuse coal and classifying cyclone feed.

Refuse Coal

Product Ash (%) = 25.48 + 2.45´A + 3.65´B - 10.34´C + 4.15´D - 4.94´B² + 2.67´C² 2.96´D² - 4.33´A´D - 4.49´B´C                                                                                                                                                                          [1]

Combustible recovery (%) = 75.06 + 16.13´B - 18.57´C + 13.28´D - 5.08´A² - 7.70´B2 - 11.71´B´D                [2]

Classifying Cyclone Feed

Product Ash (%) = 11.63 - 0.35´A + 1.06´B - 1.14´C + 0.75´D² -1.65´A´D + 0.94´B´D                                     [3]

Combustible recovery (%) = 70.49 + 3.84´A + 11.10´B - 15.40´C + 15.47´D - 9.71´B² - 6.85´D² + 7.95´A´B - 7.67´A´D                                                                                                                                   [4]

in which A is the bowl speed (hz), B the feed solids content (% by weight), C the underflow rate (lpm), and D the feed volumetric flow rate (gpm).

The parameter effects on ash and combustible recovery were analyzed using perturbation plots. The underflow rate has a pronounced effect on both product ash content and combustible recovery, while a small change in the underflow rate greatly affects product ash content and combustible recovery. The feed solids content is also an important parameter. Bowl speed had the least effect both on product ash and combustible recovery. The factors according to their importance for product ash and combustible recovery for Jader refuse can be written as:

· Underflow rate > Percent solids > Feed flow rate > Bowl speed.

Jader classifying cyclone feed;

· Underflow rate > Percent solids > Feed flow rate > Bowl speed; for product ash

· Underflow rate > Feed flow rate > Percent solids > Bowl speed; for combustible recovery

The simulations revealed that it was necessary to maintain relatively high feed solid contents with low volumetric feed rates to achieve the ultimate separation performance while treating the Jader refuse material. The studies with the Jader classifying cyclone feed showed that it was necessary to maintain low percent solids with high feed flow rate. Experiments were conducted near optimum regions as suggested by the simulation study.

Utilizing the optimum parameter values to treat the refuse and classifying cyclone material resulted in excellent separation performance relative to the theoretical washability data. For the refuse material, the mass yield achieved by the Falcon Concentrator was within 90% of the theoretical yield while producing an 8.72% clean coal concentrate. Over 80% of the pyritic sulfur was rejected which resulted in a reduction in total sulfur content from 7.21% to 2.64%. The high degree of process efficiency is further verified by the partition curve shown in Figure 2. The probable error (E_p) and specific gravity of separation (d₅₀) were calculated by washability data of the product and tailings samples (Figure 2). The E_p and the d₅₀ values were determined to be 0.12 and 1.45, respectively.

Figure 2. Partition curve obtained using the optimum operating parameter values as determined for the treatment of the Jader refuse material using the C10 Falcon concentrator; feed ash and total sulfur » 47.23% and 7.21%, respectively.

Figure 3 shows the comparison of washability and optimization data along with the results of Box-Benkhen tests obtained from the treatment of the classifying cyclone feed material. These results show that it is possible to obtain a clean coal having 9.41% ash and 2.26% total sulfur with 71.51% yield, from a feed coal having 24.50% ash and 5.54% total sulfur. The combustible recovery is about 86%. By comparing the results with washability data, the organic efficiency was determined to be approximately 90%, which indicates an excellent separation performance.

The initial scope of the project was to install and evaluate a C40 Falcon concentrator having a capacity of approximately 2000 gallons/min and 100 tons/hr. During the investigation, several modifications to the Jader Fuels preparation plant were implemented by the coal company in response to an increased demand for the clean coal product. The capacity of the plant was increased by the addition of a water-only cyclone circuit and a bank of spiral concentrators. Due to the plant modifications, the need for a Falcon Concentrator at a 100 ton/hr scale was eliminated. Current needs for the Falcon unit pertain to the treatment of spiral middling material and/or plant fine coal tailings. These applications require a Falcon Concentrator having a much lower capacity of about 5 to 20 tons/hr, which corresponds to C10 or C20 Falcon Models.

As such, the work tasks associated with the original project proposal are being modified to downgrade the Falcon model to a C10 unit. Based on the recent approval by Jader Fuels management, a C10 Falcon concentrator will be installed in the preparation and evaluated for the treatment of the spiral middling and tailing streams. The test program will entail a parametric study and a long term performance test as described in the original proposal for the larger unit. The test program is expected to be completed by the end of the extended project completion date.