RU2527964C1 - Method of controlling process of butyl rubber drying - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method consists in the supply of the wet butyl rubber crumb into an expeller, mixing in the expeller, realisation of the process of throttling, obtaining the dried rubber crumb. The preliminarily dried in the expeller crumb is supplied into an expander, after the expeller division of the crumb flow into two flows is carried out in a ratio of 9:1, one flow in a quantity of 90% of the total flow is supplied directly to the expander input, the second flow in a quantity of 10% of the total flow is irrigated on a transporter with a water solution of a drying agent, as such used is ammonium hydrocarbonate (porofor), synthesised by mixing separate flows of ammonium, carbon dioxide and water at a temperature from 0°C to +5°C in a packed column. The solution of the drying agent ammonium hydrocarbonate is cooled in a refrigeration circuit to a temperature of -3÷0°C, used in irrigation of the second flow of the rubber crumb pulp, to reduce the temperature of the rubber crumb on the output from the transporter to a temperature of +10÷+13°C. The second flow is supplied to the expander input to mix with the first flow of the crumb. Further rubber drying to the moisture content of 0.01-0.05 wt % is carried out. Control over the drying process is performed by a value of difference of temperatures of the drying agent ammonium hydrocarbonate solution before and after irrigation with it of the rubber crumb by means of an automated control system (ACS), which analyses information from sensors of the solution consumption and temperature: readings of the sensors of temperature of the drying agent ammonium hydrocarbonate solution are taken before and after irrigation with it of the rubber crumb, difference of temperatures is analysed, readings of flowmeters of consumprion of the drying agent ammonium hydrocarbonate solution are taken before and after irrigation with it of the rubber crumb, difference of the solution consumption is analysed. In case of deviation from a programmed value, the ACS sends controlling commands to change the temperature of the drying agent by changing refrigerant consumption in a refrigeration circuit. The controlling commands are sent to a circulation pump to change consumption of the flow of the drying agent ammonium hydrocarbonate solution, supplied for irrigation of the rubber crumb until the specified temperature of the crumb is achieved.EFFECT: reduction of energy consumption, increased safety due to the absence of the process with an application of high pressure, increase of rubber quality.6 ex, 3 dwg, 2 tbl

Description

The invention relates to the chemical industry, in particular to a technology for producing synthetic rubbers, in particular to processes for their isolation from solutions in hydrocarbon solvents, to a method for drying synthetic polymers, in particular polyisoprene, butyl rubber, ethylene-propylene rubbers - as the last stage of the entire process of isolation, following solution polymerization, water degassing, polymer washing and pre-packaging, to improve the drying conditions of rubber in an extrusion type apparatus for preparing final polymer particles having a very low content of volatile liquids, such as solvents, diluents, or water, and can be used in the petrochemical industry.

Known methods of drying or desolvation of polymers using extruder aggregates described in the patents:

US patent No. 2833750 (1958) relates to the removal of volatile hydrocarbons from elastomers containing from 10 to 50%, mass. solvent, using an extruder with ventilation, whereby inert gases or water are supplied to the extruder, mixed with an elastomer, and the vapor is instantly evaporated from the mixture through a ventilated section in the extruder. Then the elastomers are discharged through the die plate of the extruder.

US Pat. Nos. 3,834,440 (1974) and 3,874,090 (1975) describe an improved extrusion dryer having an adjustable variable flow rate throttling, a subsequent channel and a conveyor device after constriction, having unlimited outlet to the atmosphere.

In US patent No. 3222797 (1965) and British patent No. 965183 (1964) discloses methods of preliminary dehydration and final drying of various polymers, including elastomers, in extruder-type apparatuses.

These patents contrast their process with isothermal extrusion technology in US Pat. No. 2,833,750. According to these patents, the process works by transferring the polymer through the extruder in such a way that the temperature and pressure are gradually increased, and the polymer temperature is brought to its maximum immediately before the unloading plate. Maximum temperatures are maintained only for limited periods of time; it is indicated, for example, that the temperature cannot be exceeded from about 149 ° C to 232 ° C for more than 60 seconds. The same patents note that it may be useful to pump a small amount of steam, inert gas or superheated steam into the apparatus to increase the porosity of the polymer exiting the die, however, this process requires the use of relatively high temperatures to provide energy for drying the polymer.

In the production of synthetic elastomers, such as:

polyisoprene, butyl rubber, chlorobutyl rubber, bromobutyl rubber, SKEPT and the like, the product obtained from the polymerization process is an aqueous suspension of the polymer. To isolate the polymer from the suspension and prepare it for packaging, polymer crumb, which practically does not contain water, can be obtained in several ways.

In a typical drying process, a vibrating screen is first used, onto which an initial slurry containing 95..97 water is supplied. After the sieve, a water content in suspension of 40 ... 50% is achieved.

Further drying is provided at relatively low temperatures in the second stage, which consists of separating water from the polymer and requires the use of a dewatering extruder, which operates in the temperature range from 82 to 104 ° C. At this stage, the water content in the elastomer from 0.5 to 15%, mass. Other preliminary stages of drying are the use of extruders to remove water by compression, as well as squeezing presses, tunnel dryers, etc., or a combination thereof.

Any combination of methods in which a wet polymer is obtained containing 0.5 ... 1.0%, mass. water, preferably 0.25 ... 0.5%, mass., can be used for the practical application of the present invention.

The most critical and final step in isolating rubber from aqueous pulp is extrusion drying, which provides an elastomer that is substantially free of water. This drying technology in an extruder usually consists in heating and squeezing the elastomer in a device with a rapidly rotating screw and passing a heated mass, which includes superheated water, which, when throttled through a die, breaks the rubber and evaporates from it. The residual water content is about 0.5%, mass.

However, the above drying processes do not allow to achieve 100% drying of the polymers, since the remaining water in the amount of 0.5%, mass., Chemically related to the mass of the polymer cannot be recovered, which reduces the quality of the rubber.

The technical solution according to patent No. 4508592 dated 04/02/1985, B01D 1 \ 00, B01D 1 \ 28, US "Extrusion drying of elastomers with gas supply" was chosen as a close analogue.

The extrusion drying of wet rubber crushed crumbs in the last phase of the overall elastomer drying process is improved by using the gas supplied to the compression zone of the extruder, providing increased efficiency in the blast drying process. Rubber particles are produced having a moisture content of 0.2%, mass. The method consists in supplying wet crumbs of butyl rubber, polyisoprene, chlorobutyl rubber, bromobutyl rubber, SKEPT to the extruder and mixing so that the temperature and pressure gradually increase in the high compression zone where the drying agent (gas, water) is supplied and then the process throttling.

However, the claimed method does not allow to achieve the required degree of polymer drying, and the supply of inert gas or steam through special valves designed for high pressure at a distance of 50 mm from the die plate only leads to destabilization of the extruders and an increase in energy costs - to compress gases and increase efforts to push the polymer into the zone of greater pressure due to gas supply and a decrease in the total area of the die holes, due to the “leakage” of gas or steam into some holes and and exception of the holes of the rubber throttling process. The method also does not provide the ability to control the drying process.

The technical result of using the proposed technical solution is to reduce energy consumption, improve process safety, improve the quality of rubber.

The goal is achieved as follows.

A method for controlling the drying process of butyl rubber consists in feeding wet butyl rubber crumbs to an extruder, feeding a drying agent to an extruder, mixing in an extruder, carrying out a throttling process, obtaining dried rubber crumbs, while crumb pre-dried crumbs in the expeller are fed to the expander, and the rubber crumb flow is separated after expeller in two streams, in a ratio of 9: 1, serves one stream in the amount of 9 parts of the total directly to the expander's input, the second stream in the amount of 1 part of the total irrigated on the conveyor with an aqueous solution of a drying agent, which is used ammonium bicarbonate (porophore), synthesized by mixing separate streams of ammonia, carbon dioxide and water at a temperature of 0 ° C to + 5 ° C in a column with a nozzle,

- cool in the refrigeration circuit a solution of a drying agent of ammonium bicarbonate to a temperature of -3 ÷ 0 ° C, used in the irrigation of the second stream of rubber crumb pulp, to reduce the temperature of the rubber crumb at the outlet of the conveyor to a temperature of + 10 + 13 ° C,

- serves the second stream to the input of the expander for mixing with the first stream of chips,

- produce subsequent drying of the rubber to a moisture content of 0.01-0.05%, mass.,

- they control the drying process by the value of the temperature difference of the solution of the drying agent of ammonium bicarbonate before and after irrigating the rubber crumbs with the help of an automated control system (ACS) that analyzes information from the solution flow sensors and temperature:

- take the readings of the temperature sensors of the solution of the drying agent of ammonium bicarbonate before and after irrigation with rubber crumbs,

- analyze the temperature difference,

- take the readings of the flowmeters of the flow rate of the solution of the drying agent of ammonium bicarbonate before and after irrigation with rubber crumbs,

- analyze the difference in flow rate of the solution,

- when deviating from the programmed value through the control unit, the ACS gives control commands to change the temperature of the solution of the drying agent by changing the flow of refrigerant in the refrigeration circuit,

- direct control commands to the circulation pump to change the flow rate of the solution of the drying agent of ammonium hydrogen carbonate supplied to the irrigation of the rubber crumb pulp until the desired crumb temperature is reached.

In the drawings:

Figure 1 - General view of the installation of drying:

1 - averager,

2 - expeller (spin),

3 - conveyor,

4 - receiving distribution hopper,

5 - pipeline with the first stream of rubber pulp,

6 - pipeline with a second stream of rubber pulp,

7 - conveyor of the second stream of rubber pulp,

8 - irrigation unit,

9 - receiving hopper of the expander,

10 - expander (compression, then expansion),

11 - the finished product is dry crumb rubber.

Figure 2 - General view of the control circuit:

12 - conveyor for irrigation of crumb rubber,

13 - scales

14 - liquid level sensor in the storage tank,

15 - flow meter reverse fluid flow from the storage tank to the refrigerator,

16 - temperature sensor of the liquid from the storage tank after irrigation,

17 - liquid temperature sensor to replenish the level in the storage tank,

18 is a flow meter of fluid current to replenish the level in the storage tank,

19 - valve for regulating the flow of fluid to replenish the level in the storage tank,

20 - flow meter direct fluid flow from the refrigerator to the irrigation system,

21 - control unit

22 - liquid temperature sensor at the outlet of the refrigerator before serving in the irrigation system,

23 - refrigeration circuit

24 - circulation pump.

Figure 3 is a graph of energy consumption to Table No. 1.

Table No. 1 - expander energy consumption before and after the use of a drying agent - ammonium bicarbonate (porophore).

Table No. 2 - comparative characteristics of the methods for producing butyl rubber.

In a column with a nozzle (Rashig rings), a drying agent is synthesized - ammonium bicarbonate (NH ₄ HCO ₃ (porophore)) - by supplying separate streams: ammonia, carbon dioxide and a countercurrent of water - which is discharged by a pump into a circuit with a refrigerator, cooled by liquid ammonia , and then to the supply line of the cooled porophore solution for column irrigation and the selection of porophore solution for irrigation of a portion of the rubber pulp stream leaving the expeller in front of the expander loading hopper. The drying of rubber is sharply intensified by supplying a drying agent (porophore) to the expander, due to the fact that:

firstly, after the expeller crumbs with a very developed surface are formed;

secondly, the crumb has a very low moisture content of ~ 0.9% ... 1.5%, mass., and the solution of the drying agent (porophore) (NH ₄ HCO ₃ → NH ₄ ⁺ , HCO ₃ ^- ) dissociated into ions supplied to the irrigation to the crumb instantly it is absorbed by the pores of the electrically charged mass of the polymer and chemically binds to occluded water, which is also in the form of complexes with catalyst residues — metals of variable valency (Ti, Nd - polyisoprene, Al-butyl rubber, V - SKEPT), and subsequently, when heated in an expander, it is practically completely evaporates in a stream of sublimating ha s - ammonia, carbon dioxide, water vapor, and removed from the rubber.

The inventive method is as follows.

The crumb of rubber from several lines enters the averager 1, in which the crumb of rubber is mixed with water at a temperature of about 80 ° C. Then, rubber crumb is removed from the upper part of the averager 1 by perforated blades and fed to the expeller receiving hopper 2, in which the crumb is pressed by a screw with a variable pitch. Then the crumb with a temperature of 100-150 ° C leaves the expeller 2 with a moisture content of 2%. Next, the crumb is fed by a conveyor 3 to the receiving separation hopper 4. Then, the crumb flow is divided into two flows on the separation device:

the rubber crumb after expeller 2 is divided into two streams: one stream of 9 parts from the total stream goes directly to the input of the expander 11,

the second stream 1 part of the total flow of rubber crumb first goes through a humidification cycle with an aqueous solution of a drying agent of ammonium bicarbonate (NH ₄ CO ₃ ) in saturation unit 8, and then also enters the expander 11, mixing with the first stream of rubber crumb.

The interaction of the second stream of rubber crumb in the irrigation unit 8 with an aqueous solution of a drying agent of ammonium bicarbonate (NH ₄ HCO ₃ ) occurs on the conveyor 12. A part of the aqueous solution of the drying agent - ammonium bicarbonate flows into the storage tank under the conveyor 12 and then, after preliminary treatment, is again fed to rubber crumb irrigation. Before feeding for irrigation, the solution of the drying agent of ammonium bicarbonate (hereinafter referred to as the “solution”) is cooled to a temperature of -2 ÷ + 3 ° C so that the temperature of the second rubber stream at the outlet of saturation unit 8 and before being fed to expander 11 is 10-15 ° C .

In the receiving hopper of the expander 10, the rubber crumb flows are again mixed into one stream and enter the expander 11, in which the rubber crumb is re-dried. At the exit of the expander 11, the crumb of rubber contains an amount of moisture close to 0%.

The chips are briquetted and packaged.

The main parameter for controlling the drying process is the value of the temperature difference of the solution of ammonium bicarbonate before and after irrigation of the rubber crumb. The process control unit 21 processes the incoming values of the above temperatures and, depending on the magnitude of the temperature difference, provides control signals to the circulation pump 24 (to control the flow of the drying agent) and the refrigeration circuit 23 of the irrigation system (to control the temperature of the solution of the drying agent of ammonium bicarbonate).

The sensor type temperature sensor, from which temperature information is transmitted to the control unit 21, is installed on the pipeline with a return solution of ammonium bicarbonate.

Scales 13 for determining the weight of crumbs before irrigation with a solution and then installed on the conveyor. The flowmeters are installed on the pipelines: a flow meter for returning the liquid from the storage tank to the refrigeration unit 15, a flow meter for filling the level in the storage tank 18, a flow meter for direct liquid flow from the refrigeration unit to the irrigation system 20.

Table 1 shows the results of experiments on the effect of using drying technology using a drying agent (porophore) on the energy consumption of the expander.

As the analyzed equipment, a working expander with an electric drive with a capacity of 2.0 MW was used.

To measure the energy consumption by the expander’s electric drive, we used the three-phase CHAUVIN ARNOUX 8335 electric power quality analyzer, which was installed directly in front of the expander’s electric drive and was programmed to take 5 minutes of energy consumption readings. The energy consumption values of an expander working on a conventional technology from June 28, 2012 from 13 to 17 hours were recorded, and then the energy consumption values of an expander working on a technology using a porophore on June 30, 2012 from 13 to 17 hours were recorded. According to the measurement results, the values of the power consumption of the expander electric drive were analyzed.

As can be seen from the data of Table No. 2 (column 1) - the use of the proposed method allows to increase the load (productivity) of the separation machines - as the effective viscosity of the processed rubber mass decreases due to an increase in the content of the gas phase formed during the decomposition of the drying agent (porophore), and reduction due to this viscous friction inside the expander. Along the way, the heat release (column 7) and the destruction of the polymer are reduced.

The application of this method reduces the temperature of the total flow of crumbs at the inlet to the expander due to irrigation (cooling) of part of the flow of crumbs with a porophore solution.

Moreover, (column 7) - due to the use of porophore, which creates increased pressure in the last zone of the extruder - column 10 - there is no need to use steam supplied to the extruder jacket.

Due to the effects listed above, the total energy consumption of the separation plant is reduced from 1.9 ... 2.0 MW to 1.7 ... 1.8 MW (about 10%).

The claimed solution is an improvement in the drying process in an extruder with a throttling, namely the introduction of a drying agent (porophore) into a freshly dried elastomer at the second stage of its drying, in order to bind porophore molecules dissociated into ions due to electrostatic and chemical factors with water residues in the polymer to form the corresponding associates and their subsequent decomposition into gases with increasing temperature with the creation of a higher pressure than with conventional methods of extrusion drying of elastomers and obtaining the target product with a water content of 0.05 ... 0.025%, mass., which is not achievable using conventional technologies, because water is bound like rubber itself

, так и с теми включениями, которые присутствуют в каучуке - это металлы переменной валентности - Fe2+,3+,Ti2+3+4+,V2+3+4+5+Nd3+2+,Al3+, имеющие большой заряд на атоме и электрохимически связывающие молекулы воды (Ti⁴⁺←ОН₂).

, and with those inclusions that are present in the rubber - these are metals of variable valency - Fe2 +, 3 +, Ti2 + 3 + 4 +, V2 + 3 + 4 + 5 + Nd3 + 2 +, Al3 +, which have a large charge on the atom and electrochemically binding water molecules (Ti ⁴⁺ ← ОН ₂ ).

The claimed technical solution was developed and tested, based on the test results, it was revealed that the method allows to reduce electricity consumption, improve process safety due to the exclusion of high pressure gas supply system and improve the quality of rubber.

Table number 1 No porophore Using porophore date of Time Power consumption date of Time Power consumption 06/28/2012 13:02:58 1967763,478 06/30/2012 13:02:34 1696347,826 06/28/2012 13:07:58 1966452,174 06/30/2012 13:07:34 1702555,995 06/28/2012 13:12:58 1965846,957 06/30/2012 13:12:34 1687422.28 06/28/2012 13:17:58 1965443,478 06/30/2012 13:17:34 1716544,522 06/28/2012 13:22:58 1965140.87 06/30/2012 13:22:34 1716280,235 06/28/2012 13:27:58 1964636,522 06/30/2012 13:27:34 1702457,991 06/28/2012 13:32:58 1964636,522 06/30/2012 13:32:34 1700984,002 06/28/2012 13:37:58 1964535,652 06/30/2012 13:37:34 1720258.89 06/28/2012 13:42:58 1964838,261 06/30/2012 13:42:34 1704109,506 06/28/2012 13:47:58 1965140.87 06/30/2012 13:47:34 1711795,183 06/28/2012 13:52:58 1,965,947,826 06/30/2012 13:52:34 1706551,932 06/28/2012 13:57:58 1966956,522 06/30/2012 13:57:34 1688374,697 06/28/2012 14:02:58 1967561,739 06/30/2012 14:02:34 1699103,402 06/28/2012 14:07:58 1968368,696 06/30/2012 14:07:34 1696869,565 06/28/2012 14:12:58 1971 596,522 06/30/2012 14:12:34 1692357,529 06/28/2012 14:17:58 1972,201.739 06/30/2012 14:17:34 1722446,934 06/28/2012 14:22:58 1972,100.87 06/30/2012 14:22:34 1717857.9 06/28/2012 14:27:58 1971798,261 06/30/2012 14:27:34 1695441,325 06/28/2012 14:32:58 1971 596,522 06/30/2012 14:32:34 1699652,174 06/28/2012 14:37:58 1971899.13 06/30/2012 14:37:34 1692617,279 06/28/2012 14:42:58 1972,100.87 06/30/2012 14:42:34 1716362.811 06/28/2012 14:47:58 1971495,652 06/30/2012 14:47:34 1,699,565.217 06/28/2012 14:52:58 1970789,565 06/30/2012 14:52:34 1710754,831 06/28/2012 14:57:58 1971 596,522 06/30/2012 14:57:34 1708489,187 06/28/2012 15:02:58 1972302,609 06/30/2012 15:02:34 1712068,237 06/28/2012 15:07:58 1971 394,783 06/30/2012 15:07:34 1717242.842 06/28/2012 15:12:58 1971 596,522 06/30/2012 15:12:34 1718915,886 06/28/2012 15:17:58 1963325,217 06/30/2012 15:17:34 1708725,167 06/28/2012 15:22:58 1971 596,522 06/30/2012 15:22:34 1711455,314 06/28/2012 15:27:58 1975,328,696 06/30/2012 15:27:34 1711723,306 06/28/2012 15:32:58 1977,245,217 06/30/2012 15:32:34 1707465,645 06/28/2012 15:37:58 1975126,957 06/30/2012 15:37:34 1702695,652 06/28/2012 15:42:58 1973311,304 06/30/2012 15:42:34 1696742,308 06/28/2012 15:47:58 1971798,261 06/30/2012 15:47:34 1702761,883 06/28/2012 15:52:58 1969881,739 06/30/2012 15:52:34 1695251,066 06/28/2012 15:57:58 1971798,261 06/30/2012 15:57:34 1699826,087 06/28/2012 16:02:58 1973916,522 06/30/2012 16:02:34 1706064,409 06/28/2012 16:07:58 1973 714,783 06/30/2012 16:07:34 1708843,968 06/28/2012 16:12:58 1973 714,783 06/30/2012 16:12:34 1713294,082 06/28/2012 16:17:58 1973210,435 06/30/2012 16:17:34 1718824,421 06/28/2012 16:22:58 1973916,522 06/30/2012 16:22:34 1710499,586 06/28/2012 16:27:58 1975732,174 06/30/2012 16:27:34 1706159,045 06/28/2012 16:32:58 1977547,826 06/30/2012 16:32:34 1704782,609 06/28/2012 16:37:58 1975530,435 06/30/2012 16:37:34 1710415,961 06/28/2012 16:42:58 1965846,957 06/30/2012 16:42:34 1706464,372 06/28/2012 16:47:58 1973,109,565 06/30/2012 16:47:34 1718736,555 06/28/2012 16:52:58 1966855,652 06/30/2012 16:52:34 1705859,195

приложение 1

Annex 1

Calculation of pump and cooling circuit performance:

Q ₁ = s ₁ m ₁ dt ₁ is the amount of heat required to cool the rubber, J;

Q ₂ = c ₂ m ₂ dt ₂ is the amount of heat acquired by the solution, J;

Heat balance equation:

Q ₁ should be equal to Q ₂ , i.e. with ₁ m ₁ dt _1,

Where:

C ₁ - specific heat of rubber, J / (kg * ° C);

m ₁ is the mass of rubber, kg;

dt ₁ is the temperature difference of the rubber crumb at the inlet of the conveyor and at the outlet, ° C.

Temperature difference crumbs

dt ₁ = t _k1 -t _k2 ,

Where

t _k1 is the temperature of the rubber crumb at the inlet of the conveyor, 100-150 ° C,

and t _k2 is the temperature at the outlet of the conveyor from + 10 ÷ 13 ° C;

C ₂ is the specific heat of the solution, J / (kg * ° C);

m ₂ is the mass of the solution, kg;

dt ₂ is the temperature difference between the solution at the inlet of the conveyor and at the outlet, ° C.

Solution temperature difference

dt ₂ = t _p1 -t _p2 ,

Where

t _p1 - temperature of the return solution, ° C,

at _p2 - temperature of the solution supplied for irrigation, ° С.

The parameters by which the drying process is controlled are:

d _t2 (by temperature sensors) and m ₂ (by solution flow rate).

Solution flow rate

The specific heat of rubbers for calculations accept

2 kJ / (kg * ° C).

The specific heat capacity of water is 4.2 kJ / (kg * ° C).

Every hour, 800 kg of crumb rubber is fed to the conveyor, which

is 10 (of the total amount (8000 kg per hour)).

If you consider the situation on the conveyor every second, you can calculate the required second flow rate of the solution (in kg) to cool the rubber crumbs.

We take the specific heat of the solution equal to the heat capacity of water, d _t1 = 100 ° C, d _t2 = 10 ° C,

then the calculation of the flow rate of the solution will be as follows:

m _{2 =} c ₁ m ₁ dt ₁ / (c ₂ dt ₂ ) = 2000 * (800/60/60) * 100 / (4200 * 10) = 1.06 kg.

The required flow rate of the solution is about 1 kg per second or about 60 kg per minute.

Thus, it is possible to calculate the performance of the pump and the refrigeration unit.

Example

Obtaining ammonium bicarbonate (HCA) for use in

as a drying agent porophore.

NH ₄ HCO _{3 is} synthesized by passing equimolar amounts of NH ₃ and CO ₂ into chilled water, taken in the required excess, which is determined by the solubility of the formed salt. The corresponding solubilities in g / 100 g of H ₂ O are:

At 0 ° С - 11.9 (10% solution)

At 20 ° С - 21 (17% solution)

At 30 ° С - 27 (21% solution)

At 40 ° С - 36.6 (27% solution)

Above 40 ° C, HCA in an aqueous solution is unstable and begins to decompose. Therefore, the temperature of the working solution of the porophore should be minimal (about 0 ° C), respectively, its concentration should be about 10 (by weight.

PSA formation process exothermic:

$$C{O}_2\left(g\right)+N{H}_3\left(g\right)+H_{2}O\left(\mathrm{well}\right)=N{H}_{\mathrm{four}}HC{O}_3\text{(aq) (1)}$$

ΔNo = -98.4 kJ / mol

ΔH beats = -1.25 mJ / kg.

Therefore, it is necessary to provide adequate heat removal.

Upon decomposition of HCA at elevated temperatures, the absorption of heat occurs, respectively:

$$N{H}_{\mathrm{four}}{\text{Hco}}_{\text{3}}\left(\text{aq}\right)={\text{CO}}_{\text{2}}\left(\text{g}\right)+{\text{NH}}_{\text{3}}\left(\text{g}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{g}\right)\text{(2)}$$

ΔNo = + 142.4 kJ / mol.

ΔN beats = + 1.8 mJ / kg.

The formation of 3 mol of gas (including H ₂ O (g)) per 1 mol of HCA also occurs, which can provide the necessary overpressure in the working area of the apparatus.

The volume of the apparatus is (d = 1.5 dm, L = 50 dm).

Vobsch = L * πd ² /4=50*3.14*1.5 ^2/4 = 88 dm ^3;

V screw = 0.55 * V total = 48 dm ³ .

Working volume

Vpaб = 88-48 = 40 dm ³ .

The fill factor of the apparatus with polymer R = 0.9, hence the free volume

Vsvob = Vpab ^∗ (1-0.9) = 4 dm ³ .

The calculated water pressure during the decomposition of the porophore is 25/3 = 8.3 atm, which is slightly higher than the limit value of 7.9 atm. We believe that up to 36 kg of polymer (effective density (deff = 1.0 g / cm ³ = 1.0 kg / dm ³ ) is supplied to the apparatus in stationary mode).

The saturation of the polymer (generalized flow) with a porophore solution is 2%. Accordingly, 36 kg of wetted polymer contain 0.72 kg of HCA solution (72 g (72/79 = 0.91 mol of HCA) and 0.65 kg of H ₂ O).

The temperature in the working area of the apparatus averages 150 ° C, at the outlet - 185 ° C. With this thermal regime, the complete decomposition of the HCA is ensured according to equation (2). In this case, 0.91 mol * 3≈2.7 mol of gases is released. At an effective temperature of 170 ° C, the volume of gases is:

V = ((273 + 170) / 273) * 22.4 dm ³ / mol * mol = 98 dm ³ .

The pressure in the system is:

P = V / V _sv = 98/4 = 24.5 atm = 25 atm.

For control: at 170 ° C, the pressure of saturated water vapor is 0.792 MPa = 7.9 atm; 25/3 = 8.3 atm ≈7.9 atm. Those. in fact, due to the additional evaporation of water, the pressure in the system will not increase.

Thus, the total pressure at the outlet of the system is:

P = P + Rshnek = 25 + 25 = 50 atm.

In addition to the gases formed during the decomposition of HCA, at the outlet of the system with a sharp decrease in pressure, evaporation of almost all the superheated (up to 170 ° C) water contained in it in an amount of 0.65 kg = 36 mol (810 liters of equivalent) will be ensured, which will ensure, on the one hand, almost complete drying of the polymer (residual moisture content of 0.01%, mass.), and on the other hand, dispersion and cooling of the polymer at the outlet (at 22 ° C):

Upon evaporation of the mass of water m _H2O = 0.65 kg of water, the following amount of heat will be absorbed:

Q = m _H2O ∗ λ = 0.65 kg (2.44 MJ / kg = 1.59 MJ = 1590 kJ,

where λ is the specific heat of evaporation of water.

The mass of the polymer m _n = 36 kg is cooled to:

36 kg * 2 kJ / (kg ^∗ K) * Δt = 1590 kJ.

Δt = Q / (m _n * С _n ) = 1590 kJ / (36 kg ∗ ² kJ / kg * ° С) = 22 ° С,

where C _n is the specific heat of the polymer.

The temperature of the polymer at the outlet of the expeller is 100-150 ° C. In order to avoid decomposition of the porophore, it is proposed to divide the flow of polymer chips into two streams in a ratio of 1: 9 (stream No. 1 - 800 kg and stream No. 2 - 7200 kg). In this case, stream No. 1 is cooled by a porophore solution to 10 ° C.

I. We assume that from 100 ° C to 50 ° C, the polymer chips are cooled solely due to the decomposition of the porophore:

Q _{specific units} = -ΔN _beats = -1.8 mJ / kg.

Initial data:

m polymer = 800 kg

t of polymer = 100 ° C

t porophore = 0 ° C

t con. = 10 ° C

φ _p = 10%, mass.

Payment:

Q _floor = m _floor * C _floor * Δt = 800kg * 2 (kJ / (kg * ° C)) * (100-50) ° C = 80 MJ.

Porophore will be required:

m _then = Q _floor / Q _{specific units} = 80 MJ / 1.8 MJ / kg = 44 kg.

A porophore solution is required:

m _p = m _then pore / φп = 44 kg / 0.1 = 440 kg.

In this case, there is still water from the porophore solution in an amount of 440-44 = 396≈400 kg with a conditional temperature of 0 ° C.

We have:

800 kg of polymer (polymer t = 50 ° C);

400 kgN ₂ O (t _at -0 ° C).

Heat balance equation:

m _floor * C _floor * (50-t _con ) = m _in * C _in * (t _con -0).

From:

T _con = 24 ° C.

We get 800 kg of polymer with t = 24 ° C, and 400 kg of water (t = 24 ° C) will leave the system.

II. In order to cool the polymer chips to 10 ° C, an additional amount of solution is required (we consider the heat capacity of the solution equal to the heat capacity of pure water = 4.2 kJ / kg * ° C). The cooling process will go without decomposition of the porophore.

Heat balance equation:

m _floor * C _floor * (24-10) = m _p * C _p * (10-0);

m _p = (m _floor * C _floor * 14) / (C _p * 10) = (800 * 2 (14) / (4.2 (10) = 530 kg.

We get a pulp containing 800 kg of polymer and 530 kg of a porophore solution with a temperature of 10 ° C.

For 8000 kg of polymer, it is necessary to have a porophore solution:

m _p = m _floor * 0.02 = 8000 * 0.02 = 160 kg.

Those. must be removed from the pulp: 530-160 = 370 kg of solution.

Initial data: Brief reference book on chemistry. I.T. Goronovsky, Yu.P. Nazarenko, E.F. Nekryach. Kiev: Naukova Dumka, 1974 - 692 p.

NH ₄ HCO ₃

ΔNo arr (NH ₄ HCO _{3 tv} ) = - 849.9 kJ / mol;

ΔNo arr (NH ₄ НСО _{3 aq} ) = - 823.9 kJ / mol;

ΔNo sol. (NH ₄ HCO ₃ ) = + 26 kJ / mol;

Solubility in g / 100 g H ₂ O at t, ° C.

S ° = ll, 9 S ²⁰ = 21 S ³⁰ = 27 S ⁴⁰ = 36.6

Δ But arr _:

CO ₂ (g) = - 393.5 kJ / mol;

NH ₃ (g) = - 46.2 kJ / mol;

H ₂ O (W) = - 285.8 kJ / mol;

H ₂ O (g) = - 241.8 kJ / mol;

H ₂ O:

ΔН _isp = 44 kJ / mol = 2.44 MJ / kg;

C = 4.2 kJ / (kg ∗ ° C).

Polymer:

C = 2.0 kJ / (kg ∗ ° C).

For the formation of NH ₄ HCO ₃ :

CO ₂ (g) + NH ₃ (g) + H ₂ O (g) = NH ₄ HCO ₃ (aq)

-393.5 -46.2 -285.8 -823.9

ΔH = -92.4 kJ / mol;

ΔN _beats = -1.246 kJ / kg = -1.25 MJ / kg;

Q = + 1.25 MJ / kg.

For the decomposition process of NH ₄ HCO ₃ :

NH ₄ HCO ₃ (aq) = CO ₂ (g) + NH ₃ (g) + H ₂ O (g)

ΔNo = + 142.4 kJ / mol;

ΔN _beats = 1803 kJ / kg = 1.8 MJ / kg;

Q = -1.8 MJ / kg.

Claims (1)

A method of controlling the process of drying butyl rubber, which consists in feeding wet butyl rubber chips to an expeller, feeding a drying agent to an expander, mixing in an expander, performing a throttling process, and obtaining a dried rubber crumb, characterized in that
feed the crumb previously dried in the expeller to the expander, divide the rubber crumb stream after the expeller into two streams, in a ratio of 9: 1,
feed one stream in an amount of 90% of the total directly to the expander's input,
the second stream in an amount of 10% of the total is irrigated on the conveyor with an aqueous solution of a drying agent, which is used as ammonium bicarbonate (porophore), synthesized by mixing
separate flows of ammonia, carbon dioxide and water at a temperature from 0 ° C to + 5 ° C in a column with a nozzle,
- cool in the refrigeration circuit a solution of a drying agent of ammonium hydrogen carbonate to a temperature of -3 ÷ 0 ° C, used in the irrigation of the second stream of rubber crumb pulp, to reduce the temperature of the rubber crumb at the outlet of the conveyor to a temperature of + 10 ÷ + 13 ° C,
- serves the second stream to the input of the expander for mixing with the first stream of chips,
- produce subsequent drying of the rubber to a moisture content of 0.01-0.05%, mass.,
- they control the drying process by the value of the temperature difference of the solution of the drying agent of ammonium bicarbonate before and after irrigating the rubber crumbs with the help of an automated control system (ACS) that analyzes information from the solution flow sensors and temperature:
- take the readings of the temperature sensors of the solution of the drying agent of ammonium bicarbonate before and after irrigation with rubber crumbs,
- analyze the temperature difference,
- take the readings of the flowmeters of the flow rate of the solution of the drying agent of ammonium bicarbonate before and after irrigation with rubber crumbs,
- analyze the difference in flow rate of the solution,
- when deviating from the programmed value through the control unit, the ACS gives control commands to change the temperature of the solution of the drying agent by changing the flow of refrigerant in the refrigeration circuit,
- direct control commands to the circulation pump to change the flow rate of the solution of the drying agent of ammonium hydrogen carbonate supplied to the irrigation of the rubber crumb pulp until the desired crumb temperature is reached.

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