DE3303949A1 - METHOD FOR CONTROLLING THE VISCOSITY OF A COOL SLUDGE THAT IS THE STARTING MATERIAL FOR COAL LIQUIDATION - Google Patents

Description

DR. JOACH AT STE FFENS

DIPLOMA CHEMIST AND PATENT ADVOCATE STEUBSTRASSE10 D-8032 GRÄFELFING-MONCHEN

TELEPHONE ₁ (089) 85 23 TELEXt 52? 830iteffd

YOUR SIGN· MY CHARACTER i Gulf ~ 162

4th February 1983

The Pittsburg & Midway Coal Mining Company South Syracuse Street Englewood, Colorado 80111, U.S.A.

Method for controlling the viscosity of a raw material for coal liquefaction

serving coal sludge

For this application, priority becomes from the US patent application 346 01 of February 8, 1982 claimed.

Professional Representative before the European Patent Office

. 199520405 · Otufidit Apolhtktr · «. AnUbonk t0 MOnditn No. 00610400 (BLZ 7009OiOi)

description

The present invention relates to a method for controlling the viscosity of coal-solvent slurries. These sludges are used as raw material in coal liquefaction processes applied*

The diminishing reserves and high cost of petroleum, combined with the need for low-sulfur, clean-burning ones Fuels, led to a wide variety of research activities to develop alternative fuel sources. The abundance of indigenous coal led to intensive research into methods to convert petroleum into environmentally friendly ones To replace coal products. The most promising of these processes are the SRC processes (solvent refined coal processes) *

Among the problems encountered with the SRC process, included controlling the viscosity of the initial coal-solvent slurry. Too high viscosity slurries are difficult to pump in the process and are difficult to flow down Handling · Slurries with a low viscosity give rise to particle settling problems from the mud and an erosion of the plant.

It is true that the viscosity of the coal sludge can be reduced by reducing it control the ratio of solids: solvents, but this leads to increased plant costs because the downflow processing system must have greater capacity to handle the increased volume of feed stream. U.S. Patent 3,341,447 (Bull) is described the relationships between sludge concentration and viscosity.

In U.S. Patent No. 3,856,658 (Wölk) describes a system for the handling of problems that occur coal slurries-solvent with respect to the viscosity of.

In this process, a dilute sludge flow is first brought to a pressure / slightly above the desired reactor pressure is. The sludge is then in the downflow from the sludge pump by means of a liquid cyclone concentrated and then passed into the reactor. Because this procedure is an additional process step between the slurry pump and the reactor, not only are additional investments necessary, but it is There are also higher costs during operation.

In contrast, the method according to the invention allows the sludge viscosity to be varied while the other Variables, e.g. sludge concentration, sludge temperature and sludge shear behavior. As a result one can choose the coal concentrate temperature and other variables according to the downstream processing plant parameters and keep the viscosity in the desired range. In addition, there is no need to concentrate Sludge after passing through the sludge pump, as is necessary according to the prior art described above is required.

The coal-solvent sludge with a, controlled Viscosity is established by first pulverizing the coal. Can make a slurry of the right viscosity obtained by grinding the coal in such a way that a particle size distribution of the type is obtained that at least 80% by weight of the particles through a 30-mesh sieve (30th mesh screen) and no more than 30% by weight of the charcoal will pass through a 400 mesh screen. The ground Coal is then mixed with the solvent. Alternatively, the pulverized coal is then classified so that the largest particles through a sieve with about 8 mesh

and at least 80% by weight pass through a 30-mesh sieve (all references to particle size in both the claims as well as in the description of this application refer to the Tyler Standard Sieve Series). During this Classification, particles that pass through a sieve smaller than 400 mesh are partially removed. These Particles, hereinafter referred to as "fines", are then collected. The pulverized coal thus classified is then mixed with a hydrocarbon solvent to form a sludge. Some of the previously removed fines can then be returned to the sludge to further regulate the sludge viscosity.

Coal slurries are not Newton ¹ see liquids. The viscosity of coal slurries is determined by the coal concentration, the temperature, the shear rate and the flow time. To a lesser extent, the type of coal used can also have an influence on the sludge viscosity. According to the invention it has also been found that the particle size of the pulverized coal also has a significant influence on the viscosity of the sludge. In particular, it has been found that the fine particles resulting from the coal pulverization process greatly increase the viscosity of the sludge. Based on finding a relationship between the particle size of the coal and the viscosity of the coal sludge, the method of the present invention allows the erosive sludges of low viscosity and the inoperable sludges of high viscosities to be eliminated. In addition, the present invention allows higher temperatures to be used in the sludge mixing tank without exceeding the allowable viscosity. These advantages in turn allow improved thermal and mechanical performance when operating the coal liquefaction plant.

The following examples explain the invention without however, to limit them to this.

Examples

A number of attempts are made with a Powhatan No. 5-coal which was roughly pulverized to -30 mesh. Part of this pulverized coal is used in addition in a laboratory ball mill, consisting of a thick-walled ceramic container and two 2.5 cm steel balls ground.

Both mill products are then mixed with recycled sludge from the SRC process at 163 ° C (325 ° F). Everyone who The sludge obtained contains 30% by weight of the respective mill products. The recycled solvent sludge is composed of hydrocarbons, ash and insoluble organic substances. The composition of the recycled solvent as hydrocarbon fractions within the specified boiling ranges and the content of ash and insoluble organic substances uoS are given below:

Component weight%

Water and hydrocarbons

those below 65 ° C (150 ° F) x 0.04

boil

Boiling hydrocarbons

65-121 ° C (150-25O ° F) x 0.05

121-176 ° C (250-350 ⁰ F) 0.25

176-232 ° C (350-450 ° F) 1.31

232-287 ° C (450-550 ° F) 4.90

287-343 ° C (550-650 ° F) 8.01

343-398 ° C (650-750 ° F) 8.62

398-454 ° C (750-850 ° F) 7.42

454-482 ° C (850-900 ° F) 1.30

above 482 ° C (900 ° F) 39.17

uoS 7.55

Ashes 21.38

The viscosity of the two slurries is measured using a Brookfield Model HA viscometer at a Shear rate of 18.6 seconds at regular intervals. The viscosity values obtained as a function of the Fig. 1 shows time in the diagram.

The particle size distribution of the two milled products is as follows:

Fine mill product

see %, by
walk 60 100 100 94.2 140 87.2 200 76.8 270 59.3 325 48.6 400 41.1

Gross Mill product Meshes %, by
walk 60 96.2 100 85.0 140 68.5 200 48.1 270 · 44.2 325 39.3 400 29.5

As can be seen at once from these values, the particle size of the carbon solids in the mud is dramatic Influence on the viscosity of the sludge, this effect being intensified over time. All percentages, which are made in the present description and in the claims are percentages by weight.

Another sample from Powhatan No. 5 coal was ground and separated into fractions with the following particle size. To simplify the expression, one denotes particles, which pass through a 200-mesh sieve, for example, but not through a 270-mesh sieve, with "less than 200 stitches ".

Designation particle size (mesh)

less than 400 400+

less than 325 325-400

less than 270 270-325

less than 200 200-270

less than 150 150-200

less than 100 100-150

less than 60 60-100

Each of the fractions is then mixed with the recycled sludge as described above, whereby one Obtained sludge containing 30 wt .-% of the pulverized coal. The viscosity of each made in this way Sludge is measured with a Brookfield Viscometer Model 5 HBT and the viscosity is measured as a function of time different temperatures and shear rates.

Fig. 2 and 3 show the variation in the time-viscosity diagrams, measured at different shear rates and temperatures on a sludge, the particle sizes of has less than 200 meshes. As can be seen from each of these figures, the viscosity increases inversely to the shear rate.

The relationships between mud viscosity and temperature for a mud that has particles less than 100 mesh is shown in FIG. 4. The sludge viscosity increases with increasing sludge temperature.

Figure 5 shows time-viscosity diagrams of the fractions measured at a temperature of 163 ° C (325 ° F) and a shear rate of 18.6 seconds. ⁽⁰ F 35.O) and a shear rate of 18.6 sec ^'1 - Similarly, Figure 6 shows the viscosity values at a temperature of 177 C.. The viscosity values of each fraction at a shear rate of 37.2 seconds are shown in FIGS. 7 and 8 at temperatures of

163 ° C (325 ° F) or 177 ° C (350 ⁰ F). In Fig. 9, finally, the values of each fraction at a temperature of 177 ° C (350 ⁰ F) and a shear rate of 93 see ^{'1 is} shown. These figures show that by using larger particle sizes, higher temperature levels can be used for the same sludge viscosities. This significantly improves the overall thermal efficiency of the process, since the extent of the required cooling of the recirculated sludge stream is reduced.

As can be seen from the graphs of Figures 4-9, this is the coal particle size of the sludge the main variable affecting slurry viscosity. Accordingly, such slurries have particle sizes that does not go through a 270-mesh sieve, low initial viscosities and show relatively small increases in viscosity over time. In contrast, those sludges show with particles that have passed through a 270-mesh sieve go, higher initial viscosities and their viscosities increase considerably over time.

Though controlling the mud viscosity in any process is applicable using a pulverized coal slurry in a solvent further elucidates the present invention in connection with a coal liquefaction process. The first One step in a coal liquefaction process is to reduce the raw coal pieces to the correct size Particle size. The raw coal pieces supplied have diameters in the range from 0.6 cm (0.25 inches) to 5 cm (2 inches). The particle size of this coal must therefore be reduced to at least 8 mesh. Preferably the average particle size of the pulverized coal is such that at least 80% by weight of the Pass coal through a 30-mesh sieve.

One way how the invention can be carried out is to grind the coal in such a way that the desired particle size distribution is obtained directly as a result the grinding operation is achieved without it being necessary to add the fines in an additional stage remove.

In general, the particle size distribution will be such that at least 80% by weight of the coal will pass through a 30 mesh screen and no more than 30% by weight of the coal will pass through a 400 mesh screen. Often times it is desirable to be with one to work with coarser grist, for example one in which not more than 80% by weight of the coal passes through a 100-mesh sieve, no more than 30% by weight through a 270-mesh sieve and no more than 5% by weight through a 400-mesh sieve walk. At other times, an even coarser grist may be desired, for example one at which the distribution looks like that not more than 80 wt .-% of the coal through a 100-mesh sieve, not more than 5 wt .-% through a 270-mesh sieve and no more than 3% by weight go through a 400 mesh sieve. The exact particle size distribution for a given process is of course related with the other variables affecting mud viscosity selected. In the ability of the mud viscosity based on the particle size, which leaves a greater scope for the choice of the other, the sludge viscosity also results in influencing process parameters, the particular advantages of the present Invention.

The pulverization can be carried out by known conventional devices. For example, can you can achieve satisfactory results with a ball or jet mill. The pulverizer can operated so that oversized. Material, i.e. coal particles larger than 8 mesh, into the device for

further pulverization.

A second method of practicing the present invention involves removal following the pulverization step at least a part of the fines formed during pulverization. Dependent on of the other variables, the particles that pass through a 400-mesh sieve are removed to such an extent that that no more than 30% by weight of the coal will pass through a 400 mesh screen. In some cases, e.g. when a Particularly concentrated sludge is desired, particles that pass through a 200-mesh sieve can also partially removed. The fines can be removed by means of known standard devices. For example the pulverized coal can be classified with air and the fines then collected by means of a cyclone will. In addition, these fines, which are used to control the sludge viscosity and which too the right size to serve as fuel, as fuel to generate process heat, or alternatively be used as feed material for a coal gasification unit.

The classified pulverized coal is then mixed with the process solvent. The solvent is a petroleum or a carbon derivative distillate. Generally, the solvent is a fraction of the liquid product produced in the coal liquefaction process. A portion of the solvent can also be recycled from the liquefaction process down stream and can contain dissolved coal and coal solids. The selection of the boiling range of the distillate used depends on the operating conditions in the SRC process. The solvent y / eist generally have a boiling range of about 150 ⁰ C (3O2 ° F) to about 75O ° C (1382 ° F). A heavy distillate with a boiling range of about 230 ° C. is preferred

(446 ° F) to 480 ° C (896 ° F).

The slurry can be made by mixing the powdered ones Coal and solvent (including recycled sludge, if used) in one Boiler equipped with a shovel or other mixing device. The ratio generally used Solvent to charcoal in the SRC process is generally between about 1: 1 to about 2.5: 1.

During the production of the sludge, some of the previously removed fines are added to the sludge to make the final Adjust the sludge viscosity in the desired range. Preferably the slurry viscosity is in that Range from about 500 to 1000 centipoise. This results in a sludge that is viscous enough to prevent settling problems and to avoid erosion of the system and on the other hand is not so viscous that it can no longer be pumped.

The method according to the invention can, however, also be carried out without the final stage, i.e. the addition of the fines to the sludge will. This can be achieved by taking the average particle size of the pulverized coal varies or due to incomplete removal of the fines from the pulverized coal. Given the flexibility however, it is preferred for the controller to add a portion of the previously separated fines to the sludge in order to increase the viscosity set in the desired range. Regardless of whether the fines are returned or not, the particle size distribution of the finished sludge should fall within the ranges given above.

The sludge produced in this way is then fed into the system of the SRC process. By optimizing the sludge viscosity it is possible to work with a sludge that contains a higher percentage of solids.

This in turn results in greater thermal and mechanical efficiency in the system, since it has a smaller volume of solvent is passed through the system. In addition, the service life of the system in terms of erosion, especially with regard to the pumps and valves, if a slurry with the desired viscosity is used.

Claims (8)

Claims (1 ·) Method of making a coal-solvent slurry for use as starting material in a coal liquefaction process, characterized in that that he (a) Grind the coal so that the particle size distribution is such that at least 80% by weight of the coal passes through a 30-mesh sieve and no more than 30% by weight of the coal will pass through a 400-mesh sieve, and (b) mixing the ground coal with a solvent to form a slurry. 2. The method according to claim 1, characterized in that the particle size distribution is further defined as such will that no more than 85% by weight of the coal through a 100-mesh sieve, no more than 50% by weight of the coal through a 270-mesh sieve and no more than 30% by weight of the coal will pass through a 400 mesh screen. 3. The method according to claim 2, characterized in that the particle size distribution is further defined will that not more than 80% by weight of the coal through a 100-mesh sieve, no more than 30% by weight of the coal through a 270 mesh sieve and no more than 5% by weight of the coal will pass through a 400 mesh screen. 4. The method according to claim 3, characterized in that the particle size distribution is further defined as such will that not more than 80% by weight of the coal through a 100-mesh sieve, not more than 5% by weight of the coal through a 270-mesh sieve and not more than 3% by weight pass the coal through a 400-mesh sieve. 5. A method of making a coal-solvent slurry for use as a starting material in a coal liquefaction process with a controllable viscosity, characterized in that one (a) pulverize the coal; (b) the coal classified so that the particles with the maximum size passed through an 8-mesh sieve, at least 80% by weight of the particles pass through a 30-mesh sieve and that the fine particles pass through a 400-mesh sieve are partially removed to such an extent that no more than 30% by weight of the any remaining particles pass through a 400-mesh sieve; (c) collecting the fine particles following the classification step, and (d) the classified pulverized coal with a hydrocarbon solvent to form a mud mixes. 6. The method according to claim 5, characterized in that the ratio of solvent to coal is between about 1: 1 and 2.5: 1. 7. The method according to claim 6, characterized in that a proportion of the fine particles from the pulverized Coals have been removed, returned to the sludge to maintain its viscosity to control the mud. 8. Method for controlling the viscosity of a coal • Solvent sludge for use as a feedstock in a coal liquefaction process, thereby marked that one (a) pulverize the coal; (b) The coal is classified so that the particles are of maximum size through an 8-mesh sieve and at least 80% by weight of the particles pass through a 30-mesh sieve and the fine particles pass through a 400-mesh sieve, partially removed to such an extent that no more than 30% by weight the remaining particles pass through a 400-mesh sieve; (c) collecting the fines following the classification step; (d) the classified pulverized coal with a hydrocarbon solvent to form a mud mixes, and (e) a portion of the fine particles previously removed from the pulverized coal back into guides the sludge mixture to control the sludge viscosity. 9 * Method according to claim 8, characterized in that that the ratio of solvent to coal is between about 1: 1 and about 2.5: 1. 10 "SRC method, in which go from a pulverized coal of which at least 80 wt .-% through a 30-mesh sieve, and a solvent forms a slurry and the dissolved carbon at an elevated temperature with hydrogen to reaction takes , characterized in that one -A- (a) From the pulverized coal fine particles that pass through a 400-mesh sieve, partially up removed to such an extent that no more than 30% by weight of the remaining coal passes through one 400-mesh sieve go; (b) collects the fines; (c) the pulverized coal with a hydrocarbon solvent mixes to form a sludge, and (d) a portion of the fines previously removed from the pulverized coal to the sludge mixture gives / to control viscosity.