Coal grinding and drying system with superheated steam as circulating medium

Abstract

The utility model discloses a coal grinding and drying system taking superheated steam as a circulating medium. The system comprises a coal bunker (1), a weighing coal feeder (2), a coal grinding machine (3), a pulverized coal collector (4), a circulating fan (6), a heating device (7) and the coal grinding machine (3) which are communicated in sequence, wherein an exhaust tail gas outlet is formed in a pipeline through which the pulverized coal collector (4) is communicated with the circulating fan (6), a starting gas inlet is formed in a pipeline through which the heating device (7) is communicated with the circulating fan (6), and when the pulverized coal drying system operates normally, the starting gas inlet is in a completely closed state. The system can reduce the amount of exhaust tail gas of an existing coal grinding and drying system, the exhaust tail gas mainly contains steam, and follow-up heat and moisture recovery is facilitated.

Description

Technical Field

[0001] The utility model relates to the technical field of coal chemical industry, in particular to a coal grinding and drying system using superheated steam as a circulating medium. Background Art

[0002] Pulverized coal gasification technology is an advanced technology that can cleanly and efficiently convert various types of solid coal into a gaseous mixture of carbon monoxide and hydrogen. Its basic principle is to grind coal into dry coal powder, continuously feed it into a gasifier with inert gas, and react under high temperature and high pressure conditions to generate raw coal gas containing carbon monoxide and hydrogen.

[0003] The pulverized coal gasification technology requires that the typical moisture content of the pulverized coal entering the gasifier is ≤5wt% (mass percentage). For this reason, the coal needs to be dried. Existing coal grinding and drying systems generally use hot inert gas (the circulating medium is mainly inert gas, and the proportion of inert gas is generally greater than 60vol% (volume percentage)). The inert gas is generally nitrogen, carbon dioxide and oxygen (oxygen content is less than 8vol%). The coal grinding and drying system uses hot inert gas at a temperature of 150-350°C to dry the coal powder. In order to maintain the moisture balance of the system, part of the exhaust gas needs to be discharged. The exhaust gas contains about 30vol%-40vol% water and the temperature is about 105°C. The existing typical coal grinding and drying system that uses hot inert gas circulation has the following problems:

[0004] 1. The hot inert gas circulation coal grinding drying system needs to continuously replenish inert gas, which is generally derived from nitrogen from air separation and air pressurized by a blower. Nitrogen is separated by deep cold separation in the air separation unit. The energy consumption of deep cold separation is very high, and the blower also consumes electricity. The consumption of inert gas increases the operating cost of the coal grinding drying system;

[0005] 2. Inert gases are mainly nitrogen and oxygen. Nitrogen and oxygen have small specific heat. The coal grinding and drying system requires a large circulating gas volume and a high hot inert gas temperature, which increases the energy consumption of the system.

[0006] 3. In order to maintain the moisture balance of the system, the coal grinding and drying system needs to continuously discharge tail gas, which contains more than 60 vol% inert gas. The temperature of the inert gas discharged with the tail gas is about 105°C, which loses a lot of heat.

[0007] 4. More than 60 vol% of the exhaust gas is inert gas, of which steam is less than 40 vol%. The presence of a large amount of inert gas increases the difficulty of water recovery and increases the investment in subsequent recovery equipment. Utility Model Content

[0008] The researchers of the utility model have focused on studying the problems existing in the existing coal grinding and drying system using hot inert gas circulation, and proposed a coal grinding and drying system using superheated steam as the circulating medium, which solves the problems of high energy consumption, waste of water resources and environmental pollution existing in the existing coal grinding and drying system using hot inert gas circulation.

[0009] The utility model provides a coal grinding and drying system using superheated steam as a circulating medium, wherein the coal grinding and drying system comprises a coal bunker, a weighing coal feeder, a coal grinding machine, a coal powder collector, a circulating fan, a heating device and the coal grinding machine which are connected in sequence; wherein an outlet for exhaust gas is arranged in a pipeline connecting the coal powder collector and the circulating fan, and a starting gas inlet is arranged in a pipeline connecting the heating device and the circulating fan, and when the coal grinding and drying system is operating normally, the starting gas inlet is in a completely closed state.

[0010] In the system of the utility model, the coal mill, the coal powder collector, the circulating fan, the heating device and the coal mill are connected in a closed loop in sequence to form a gas circulation passage, that is, the coal mill drying system of the utility model includes a system part composed of the coal mill, the coal powder collector, the circulating fan, the heating device and the coal mill connected in a closed loop in sequence. In the system of the utility model, under normal operating conditions, the circulating medium component of the coal mill drying system is mainly superheated steam (and may also contain a small amount of unavoidable inert gas). Under this normal operating condition, the starting gas inlet of the coal mill drying system is maintained in a completely closed state until all the coal to be dried is completely dried.

[0011] The coal mill drying system of the utility model, when the system is started, as the coal intake per unit time of the coal mill gradually increases, the outlet temperature of the coal mill will decrease due to the increase in the evaporation of water in the coal, and it is necessary to increase the load of the heating device accordingly to maintain the stable outlet temperature of the coal mill. The amount of the starting gas introduced is gradually reduced, and the pressure of the circulating medium at the inlet of the circulating fan is kept stable while "gradually reducing" the amount of the starting gas introduced. If the pressure of the circulating medium at the inlet of the circulating fan decreases, the speed of reducing the amount of the starting gas introduced is reduced. Through the circulation of the circulating gas in the system, the water evaporated from the coal is heated by the heating device to form superheated steam, and the starting gas is gradually replaced by the superheated steam until the system reaches a normal operating state in which the superheated steam contained in the circulating gas is higher than 50vol%, and the introduction of the starting gas is stopped. It can be considered that "mainly superheated steam" means that the circulating gas of the system contains more than 50vol% superheated steam, which varies depending on the amount of inert gas entering the system. For example: if 5000m 3 / h inert gas plus 18850m 3 / h flue gas enters the system, "mainly superheated steam" means that superheated steam accounts for 53.01vol%; if 5000m 3 / h inert gas enters the system, “mainly superheated steam” means that superheated steam accounts for 80.57vol%; if all inert gases can be avoided from entering the system, “mainly superheated steam” means that superheated steam accounts for nearly 100vol%.

[0012] In practice, the circulating medium of the coal grinding and drying system of the utility model may also include a small amount of other inert gases, which may be one or more of the following: (1) gases other than water vapor brought into the coal grinding and drying system by coal; (2) gases other than water vapor released due to heating of coal; (3) air leaked into the system; (4) gases other than water vapor that enter the system due to equipment or process reasons. These small amounts of other inert gases are gases that passively and inevitably enter the circulating medium due to equipment and / or process reasons. These other inert gases other than superheated steam are detrimental to the operation of the system of the utility model and should be reduced as much as possible.

[0013] In the system of the utility model, the coal grinding and drying system also includes a screw conveyor, one end of which is connected to the bottom of the coal powder collector to convey the dry coal powder collected at the bottom of the coal powder collector to the subsequent process.

[0014] In one embodiment of the system of the utility model, the heating device is used to heat the circulating medium to increase the temperature of the circulating medium, and the heating device is selected from any one or a combination of the following:

[0015] (1) an electric heater, that is, the circulating medium enters the electric heater, and the electric heater consumes electrical energy to release heat to heat the circulating medium;

[0016] (2) a steam heater, i.e., the circulating medium enters the steam heater, and the steam releases heat in the steam heater to heat the circulating medium;

[0017] (3) a heating furnace, i.e., the circulating medium enters the coil in the heating furnace, and the fuel gas burns outside the coil in the heating furnace to release heat to heat the circulating medium in the coil;

[0018] (4) Hot blast furnace, that is, the circulating medium enters the hot blast furnace, the fuel gas burns in the hot blast furnace, and high-temperature flue gas is generated. The high-temperature flue gas mixes with the circulating medium entering the hot blast furnace to increase the temperature of the circulating medium. When using a hot blast furnace, the combustion flue gas will enter the circulating medium, and the inert gas will enter the circulating medium due to process reasons. However, compared with the existing typical hot inert gas circulation coal grinding and drying system, it still has greater technical advantages.

[0019] In a further embodiment of the system of the utility model, the heating furnace or hot blast furnace uses clean fuel and low-nitrogen burners to reduce pollutants in exhaust gas and reduce environmental pollution.

[0020] In one embodiment of the system of the utility model, the coal grinding and drying system is a closed system so as to reduce the leakage of air into the system and minimize the inert gas entering the coal grinding and drying system due to equipment reasons.

[0021] In one embodiment of the system of the utility model, the coal grinding and drying system is a system that introduces a startup gas from the time of startup to before normal operation, and the startup gas is selected from one of nitrogen and carbon dioxide, or a mixture of the two.

[0022] In one embodiment of the system of the utility model, an outlet for exhaust gas is provided in the pipeline connecting the coal powder collector and the circulating fan of the coal grinding and drying system. In other words, the outlet position of the exhaust gas is set before the circulating fan. The system of the utility model is different from the prior art. When the system of the prior art is in operation, there is generally a slight negative pressure in front of the circulating fan, and it is impossible to set an outlet for exhaust gas in front of the circulating fan. The operating pressure of the system of the utility model is improved as a whole. It is a slight positive pressure before the pressure is increased, and after the pressure is increased, it is more conducive to the condition of setting an outlet for exhaust gas in front of the circulating fan. The outlet position of the exhaust gas is set in front of the circulating fan, which reduces the amount of air entering the circulating fan, reduces the power of the circulating fan, and can save energy.

[0023] In one embodiment of the system of the utility model, when the pulverized coal drying system is started and operated, the pressure at the inlet of the circulating fan is 0.001kPaG to 30kPaG, preferably 1kPaG to 10kPaG. When the pulverized coal drying system is in operation, the position with the lowest pressure is the inlet of the circulating fan, and the pressure at the inlet of the circulating fan is 0.001kPaG to 30kPaG, preferably 1kPaG to 10kPaG. In the utility model, when the system is in operation, the pressure at the inlet of the circulating fan of the pulverized coal drying system is a slightly positive pressure to prevent outside air from entering the pulverized coal drying system. In the utility model, when the system is in operation, the pressure of the circulating gas is not exactly the same as that of the prior art. When the system of the prior art is in operation, it is generally a slightly negative pressure before the pressure is increased, and it is generally a slightly positive pressure after the pressure is increased; the operating pressure of the system of the utility model is improved as a whole, and it is a slightly positive pressure before the pressure is increased, and the pressure is higher after the pressure is increased, so that outside air can be prevented from entering the pulverized coal drying system due to leakage, and other inert gases other than water vapor can be prevented from being mixed into the circulating gas. In the present invention, for the circulating gas of the entire circulating system, the pressure is the lowest at the inlet of the circulating fan before the pressure is increased, and the pressure is the highest at the outlet of the circulating fan after the pressure is increased.

[0024] In one embodiment of the system of the utility model, the sealing gas of the coal mill is superheated steam. In the utility model, if technically permitted, the coal mill selects superheated steam as the sealing gas of the coal mill. In the utility model, certain positions in the coal mill (such as bearings) need to be filled with high-pressure gas to prevent coal powder from entering. The high-pressure gas is the sealing gas of the coal mill. The pressure of the sealing gas of the coal mill is relatively high, which must be higher than the pressure of the circulating medium entering the coal mill by more than 30kPa to play a role in protecting the coal mill.

[0025] In the present invention, "steam" is also referred to as "water vapor".

[0026] In the present invention, "vol %" means volume ratio.

[0027] In the present invention, "wt %" means mass ratio.

[0028] The utility model has the following beneficial effects:

[0029] 1. The coal grinding and drying system of the utility model is a system in which the starting gas inlet is in a completely closed state during normal operation; in other words, during normal operation, the circulating medium in the system mainly adopts superheated steam formed by the heated evaporation of coal feed, and during normal operation, the system no longer opens the starting gas inlet manually, and no amount of starting gas is introduced.

[0030] 2. In order to minimize the amount of inert gas other than superheated steam entering the circulating medium of the system, the following measures are designed:

[0031] (1) The position with the lowest pressure in the coal grinding and drying system is the inlet position of the circulating fan. The operating pressure at the inlet position of the circulating fan is between 0.001 kPaG and 50 kPaG, preferably between 1 kPaG and 10 kPaG, so as to prevent external air from entering the system due to leakage.

[0032] (2) In order to prevent outside air from entering the system due to leakage and to prevent the circulating medium from leaking into the environment, a closed system is also adopted, that is, the coal grinding and drying system is a closed system.

[0033] (3) Superheated steam is used to replace other inert gases that enter the coal pulverizing and drying system due to equipment and / or process reasons to the greatest extent possible, and the inert gases that enter the coal pulverizing and drying system due to equipment reasons are minimized to the greatest extent possible. For example, in the system of the present invention, the coal pulverizer selects superheated steam as the sealing gas of the coal pulverizer.

[0034] (4) In the system of the present invention, the heating device is selected from an electric heater, a partition heat exchanger or a heating furnace with steam as a heat source, or a series combination thereof, so as to avoid introducing other inert gases except superheated steam into the system of the present invention, and to minimize other inert gases entering the coal grinding drying system due to equipment and / or process reasons. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the structure of a coal grinding and drying system using superheated steam as a circulating medium provided by the utility model (general scheme);

[0036] Figure 2 A schematic diagram of the structure of a coal grinding and drying system using superheated steam as a circulating medium provided in Example 1 of the utility model (electric heater solution);

[0037] Figure 3 A schematic diagram of the structure of a coal grinding and drying system using superheated steam as a circulating medium (steam heater solution) provided in Example 2 of the utility model;

[0038] Figure 4 A schematic diagram of the structure of a coal grinding and drying system using superheated steam as a circulating medium (heating furnace solution) provided in the third embodiment of the present utility model;

[0039] Figure 5 This is a schematic structural diagram of a coal grinding and drying system using superheated steam as a circulating medium (hot blast furnace solution) provided in Example 4 of the utility model.

[0040] Figure 6 The schematic diagram of the hot inert gas circulation coal grinding drying system in the prior art.

[0041] Description of reference numerals:

[0042] 1- coal bunker; 2- weighing coal feeder; 3- coal mill; 4- coal powder collector; 5- screw conveyor; 6- circulating fan; 7- heating device; 8- electric heater; 9- steam heater; 10- heating furnace; 11- hot air furnace; 12- combustion air fan; 13- dilution air fan. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the utility model clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. The following description is only for the purpose of explanation and is by no means understood as a limitation on the system for grinding and drying coal with superheated steam as the circulating medium described in the utility model. It should be understood that the content disclosed in the utility model also includes any solution and all variations that can be learned from the teachings provided herein.

[0044] Comparative Example

[0045] The coal grinding and drying system of a pulverized coal gasification unit dries 100 tons / hour of wet coal with a water content of 20wt% to a water content of 4wt%. The typical hot inert gas circulation coal grinding and drying system is used for drying. Figure 6 shown.

[0046] The circulating fan 6 of the coal mill drying system is started, and nitrogen is introduced at the outlet of the circulating fan 6. The gas in the system and the introduced nitrogen are circulated under the action of the circulating fan 6. In order to stabilize the pressure at the inlet of the circulating fan 6 at -6kPaG (slightly negative pressure), part of the circulating gas is discharged from the system at the outlet of the circulating fan 6 (6kPaG (slightly positive pressure)). When the oxygen content of the circulating gas in the system is lower than 8vol%, the hot blast furnace 11 is started to heat the circulating gas. When the circulating gas temperature at the outlet of the coal mill 3 reaches 105℃, the wet coal containing 20wt% of water enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2.

[0047] The coal is ground into coal powder with the particle size meeting the requirements in the coal mill 3.

[0048] After coal is fed into the coal mill 3, the temperature of the circulating gas at the outlet of the coal mill 3 will decrease due to the evaporation of the water in the coal. The load of the hot blast furnace 11 is increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 105°C. The amount of coal fed into the coal mill 3 is gradually increased until it reaches 100 tons / hour. In the process of increasing the amount of coal fed into the coal mill 3, the load of the hot blast furnace 11 is simultaneously increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 105°C. The water evaporated from the coal is converted into steam and enters the circulating gas. When the steam content in the circulating gas at the outlet of the coal mill 3 reaches 38vol%, the dilution air fan 13 is turned on to pass the pressurized air into the system at the inlet of the circulating fan 6. The amount of dilution air introduced is determined according to the steam content of the circulating gas to keep the steam content in the circulating gas at the outlet of the coal mill 3 not higher than 38vol%. At the same time, nitrogen should also be continuously introduced into the system to keep the oxygen content of the circulating gas at the outlet of the coal mill 3 not higher than 8vol%. Under normal operating conditions, the superheated steam content in the exhaust gas is 36.20 vol%, and the oxygen content is 7.06 vol%; the circulating gas flow rate entering the pulverizer is 222.2 tons / hour (equivalent to 2.67 kg circulating medium / 1.0 kg dry coal powder) and the temperature is 300°C.

[0049] The circulating medium enters the coal mill 3 and blows the coal powder into the coal powder collector 4.

[0050] During the coal grinding and blowing process, the circulating medium heats the coal powder, converting the moisture it contains into gaseous state and entering the circulating medium. The temperature of the circulating medium leaving the coal mill 3 is 105°C, and the superheat is 33°C. A filter is set in the coal powder collector 4. After the circulating medium leaves the coal powder collector 4 through the filter, it enters the circulating fan 6. 83.33 tons / hour of dry coal powder containing 4wt% of water is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 for pressurization, part of it (28.11%) leaves the coal grinding and drying system as exhaust gas, and the remaining part (71.89%) is mixed with nitrogen and dilution air from the dilution air fan 13 and enters the hot air furnace 11 for heating. 7165Nm of nitrogen is introduced into the system 3 / h, dilution air introduced into the system and coal mill sealing air 11254Nm 3 / h, the hot air furnace flue gas entering the system is 19175Nm 3 / h (including inert gas 16225Nm 3 / h, water content 2.37 tons / hour), since the front of the circulating fan 6 is in a slightly negative pressure state, the leakage air entering the system is 7106Nm 3 / h, these inert gases entering the system will eventually be discharged from the system through the exhaust gas. The power of the circulating fan 6 is 1528kW, and the heat load of the hot air furnace 11 is 12.61Gcal / hour. Considering the thermal efficiency of the hot air furnace of 90%, 14.02Gcal / hour of fuel gas is required. If natural gas is used as fuel, 1639Nm of natural gas is required. 3 / h. The circulating medium heated by the hot blast furnace 11 has a temperature of 300°C and enters the coal mill 3 again to complete a cycle.

[0051] After calculation, the exhaust gas is 73.09 tons / hour. The specific exhaust gas composition and flow data are shown in Table 1 below.

[0052] Table 1

[0053] Components Volume composition, vol% <![CDATA[Volumetric flow rate, Nm 3 / h]]> Mass composition, mass% Mass flow, kg / h <![CDATA[H2O]]> 36.20 23686 26.05 19038 <![CDATA[N2]]> 54.48 35651 60.96 44557 <![CDATA[O2]]> 7.06 4622 9.03 6599 <![CDATA[CO2]]> 2.25 1475 3.96 2896 total 100.00 65434 100.00 73090

[0054] It can be seen from Table 1 above that the exhaust gas is 73.09 tons / hour (equivalent to 65,400 standard cubic meters / hour), contains 19.04 tons / hour of water, and the temperature of the exhaust gas is about 105°C. It can be seen that the exhaust gas contains a large amount of water and heat. Since the water vapor content in the exhaust gas is only 36.20 vol%, and the inert gas content is as high as 63.80 vol%, it is difficult to recover the water and heat in the exhaust gas. A large amount of exhaust gas emissions also cause environmental pollution.

[0055] Example

[0056] Figure 1 The schematic diagram of the structure of the coal grinding and drying system with superheated steam as the circulating medium provided by the utility model (general scheme) is as follows: Figure 1 As shown in the figure, coal enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2, and the coal is ground into coal powder with the required particle size in the coal mill 3. The hot circulating medium with superheated steam as the main component enters the coal mill 3, and blows the coal powder into the coal powder collector 4. During the coal grinding and blowing process, the hot circulating medium heats the coal powder, so that the moisture contained in it is converted into gaseous steam and enters the circulating medium. A filter is set inside the coal powder collector 4. After the circulating medium leaves the coal powder collector 4 through the filter, part of it leaves the coal grinding drying system as the exhaust gas, and the remaining part enters the circulating fan 6. The dried coal powder is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 to increase the pressure, it enters the heating device 7 for heating. The heated circulating medium leaves the heating device 7 and enters the coal mill 3 again, completing a cycle process.

[0057] The following is a specific example to illustrate the coal grinding and drying system provided by the utility model using superheated steam as the circulating medium.

[0058] Example 1: Electric heater heating device

[0059] In this embodiment 1, an electric heater is used to dry 100 tons / hour of wet coal containing 20 wt% of water to 4 wt% of water. Figure 2 shown.

[0060] The circulating fan 6 of the coal mill drying system is started, and the starting gas nitrogen is introduced at the outlet of the circulating fan 6. The gas in the system and the introduced starting gas are circulated under the action of the circulating fan 6. In order to stabilize the inlet pressure of the circulating fan 6 at 3kPaG, part of the circulating gas is discharged from the system at the inlet of the circulating fan 6. When the oxygen content of the circulating gas in the system is lower than 8vol%, the electric heater 8 is started to heat the circulating gas. When the temperature of the circulating gas at the outlet of the coal mill 3 reaches 126℃, the wet coal with a water content of 20wt% enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2.

[0061] The coal is ground into coal powder with the particle size meeting the requirements in the coal mill 3.

[0062] After coal is fed into the coal mill 3, the temperature of the circulating gas at the outlet of the coal mill 3 will decrease due to the evaporation of the water in the coal. The load of the electric heater 8 is increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The coal feeding amount of the coal mill 3 is gradually increased until it reaches 100 tons / hour. In the process of increasing the coal feeding amount of the coal mill 3, the load of the electric heater 8 is simultaneously increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The water evaporated from the coal is converted into steam and heated to become superheated steam, which gradually replaces the starting gas, so that the circulating medium transitions to superheated steam as the main medium. The amount of starting gas introduced is gradually reduced at a rate of 5% / hour. After about 20 hours, the introduction of starting gas is completely stopped, and the coal mill drying system enters a normal operating state. Under normal operating conditions, the superheated steam content in the exhaust gas is 80.57vol%, and the circulating gas flow rate entering the coal mill is 222.2 tons / hour (equivalent to 2.67kg circulating medium / 1.0kg dry coal powder) and the temperature is 275°C.

[0063] The circulating medium enters the coal mill 3 and blows the coal powder into the coal powder collector 4.

[0064] During the coal grinding and blowing process, the circulating medium heats the coal powder, converting the water contained in it into gaseous state and entering the circulating medium. The temperature of the circulating medium leaving the coal mill 3 is 126°C and the superheat is 33°C. A filter is set in the coal powder collector 4. After the circulating medium passes through the filter and leaves the coal powder collector 4, most of it (90.58%) enters the circulating fan 6, and the remaining part leaves the coal grinding drying system as the exhaust gas. 83.33 tons / hour of dry coal powder containing 4wt% of water is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 for pressure increase, it enters the electric heater 8 for heating. The power of the circulating fan 6 is 1886kW, and the heat load of the electric heater 8 is 11.93Gcal / hour. Considering the thermal efficiency of the electric heater of 95%, the power of the electric heater 8 is 14605kW. The circulating medium temperature after being heated by the electric heater 8 is 275°C and enters the coal mill 3 again, completing a cycle.

[0065] Considering the inert gas entering the system due to equipment and process reasons, 5000Nm 3 / h. After calculation, the exhaust gas is 23.1 tons / hour. The specific exhaust gas composition and flow rate data are shown in Table 2 below.

[0066] Table 2 Composition and flow rate of exhaust gas

[0067] Components Volume composition, vol% <![CDATA[Volumetric flow rate, Nm 3 / h]]> Mass composition, mass% Mass flow, kg / h <![CDATA[H2O]]> 80.57 20735 72.14 16666 <![CDATA[N2]]> 15.35 3950 21.37 4937 <![CDATA[O2]]> 4.08 1050 6.49 1499 <![CDATA[CO2]]> 0.00 0 0.00 0 total 100.00 25735 100.00 23102

[0068] As shown in Table 2 above, after the application of the utility model system, the water content in the exhaust gas is as high as 80.57 vol%, which is more than double the water content of the conventional system (36.20 vol%). The high water content in the exhaust gas reduces the difficulty of heat recovery and water resource recovery in the subsequent process; the exhaust gas is 23.1 tons / hour, which is equivalent to one-third of the exhaust gas volume of the conventional system (73.09 tons / hour), which reduces the investment in heat recovery and water resource recovery in the subsequent process, and also reduces waste gas emissions to protect the environment. The above data is based on 5000Nm 3 / h inert gas entering the system. If the inert gas entering the system is further reduced, the water content in the exhaust gas will further increase and the flow rate of the exhaust gas will further decrease.

[0069] Example 2: Steam heater heating device

[0070] In this Example 2, a steam heater is used to dry 100 tons / hour of wet coal containing 20 wt% of water to 4 wt% of water. Figure 3 shown.

[0071] The circulating fan 6 of the coal mill drying system is started, and the starting gas nitrogen is introduced at the outlet of the circulating fan 6. The gas in the system and the introduced starting gas are circulated under the action of the circulating fan 6. In order to stabilize the inlet pressure of the circulating fan 6 at 3kPaG, part of the circulating gas is discharged from the system at the inlet of the circulating fan 6. When the oxygen content of the circulating gas in the system is lower than 8vol%, the steam heater 9 is started to heat the circulating gas. When the temperature of the circulating gas at the outlet of the coal mill 3 reaches 126℃, the wet coal with a water content of 20wt% enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2.

[0072] The coal is ground into coal powder with the particle size meeting the requirements in the coal mill 3.

[0073] After coal is fed into the coal mill 3, the temperature of the circulating gas at the outlet of the coal mill 3 will decrease due to the evaporation of the water in the coal. The load of the steam heater 9 is increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The coal feeding amount of the coal mill 3 is gradually increased until it reaches 100 tons / hour. In the process of increasing the coal feeding amount of the coal mill 3, the load of the steam heater 9 is simultaneously increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The water evaporated from the coal is converted into steam and heated to become superheated steam, which gradually replaces the starting gas, so that the circulating medium transitions to superheated steam as the main medium. The amount of starting gas introduced is gradually reduced at a rate of 5% / hour. After about 20 hours, the introduction of starting gas is completely stopped, and the coal mill drying system enters a normal operating state. Under normal operating conditions, the superheated steam content in the exhaust gas is 80.57vol%, and the circulating gas flow rate entering the coal mill is 222.2 tons / hour (equivalent to 2.67kg circulating medium / 1.0kg dry coal powder) and the temperature is 275°C.

[0074] The circulating medium enters the coal mill 3 and blows the coal powder into the coal powder collector 4.

[0075] During the coal grinding and blowing process, the circulating medium heats the coal powder, converting the water contained in it into gaseous state and entering the circulating medium. The temperature of the circulating medium leaving the coal mill 3 is 126°C and the superheat is 33°C. A filter is set in the coal powder collector 4. After the circulating medium passes through the filter and leaves the coal powder collector 4, most of it (90.58%) enters the circulating fan 6, and the remaining part leaves the coal grinding drying system as the exhaust gas. 83.33 tons / hour of dry coal powder containing 4wt% of water is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 for pressure increase, it enters the steam heater 9 for heating. The power of the circulating fan 6 is 1886kW, the heat load of the steam heater 9 is 11.93Gcal / hour, and 10MPaG steam is used as the heat source. Considering the thermal efficiency of the steam heater of 90%, 42.1 tons / hour of 10MPaG steam is required. The circulating medium temperature after being heated by the steam heater 9 is 275°C and enters the coal mill 3 again, completing a cycle.

[0076] Considering the inert gas entering the system due to equipment and process reasons, 5000Nm 3 / h, after calculation, the exhaust gas is 23.1 tons / hour. The specific exhaust gas data are shown in Table 3 below.

[0077] Table 3 Composition and flow rate of exhaust gas

[0078] Components Volume composition, vol% <![CDATA[Volumetric flow rate, Nm 3 / h]]> Mass composition, mass% Mass flow, kg / h <![CDATA[H2O]]> 80.57 20735 72.14 16666 <![CDATA[N2]]> 15.35 3950 21.37 4937 <![CDATA[O2]]> 4.08 1050 6.49 1499 <![CDATA[CO2]]> 0.00 0 0.00 0 total 100.00 25735 100.00 23102

[0079] As shown in Table 3 above, after the application of the utility model system, the water content in the exhaust gas is as high as 80.57 vol%, which is more than double the water content of the conventional system (36.20 vol%). The high water content in the exhaust gas reduces the difficulty of heat recovery and water resource recovery in the subsequent process; the exhaust gas is 23.1 tons / hour, which is equivalent to one-third of the exhaust gas volume of the conventional system (73.09 tons / hour), which reduces the investment in heat recovery and water resource recovery in the subsequent process, and also reduces waste gas emissions to protect the environment. The above data is based on 5000Nm 3 / h inert gas entering the system. If the inert gas entering the system is further reduced, the water content in the exhaust gas will further increase and the flow rate of the exhaust gas will further decrease.

[0080] Example 3: Heating furnace heating device

[0081] In this embodiment 3, a heating furnace is used to dry 100 tons / hour of wet coal containing 20 wt% of water to a water content of 4 wt%. Figure 4 Shown

[0082] The circulating fan 6 of the coal mill drying system is started, and the starting gas nitrogen is introduced at the outlet of the circulating fan 6. The gas in the system and the introduced starting gas are circulated under the action of the circulating fan 6. In order to stabilize the inlet pressure of the circulating fan 6 at 3kPaG, part of the circulating gas is discharged from the system at the inlet of the circulating fan 6. When the oxygen content of the circulating gas in the system is lower than 8vol%, the heating furnace 10 is started to heat the circulating gas. When the temperature of the circulating gas at the outlet of the coal mill 3 reaches 126℃, the wet coal with a water content of 20wt% enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2.

[0083] The coal is ground into coal powder with the particle size meeting the requirements in the coal mill 3.

[0084] After coal is fed into the coal mill 3, the temperature of the circulating gas at the outlet of the coal mill 3 will decrease due to the evaporation of the water in the coal. The load of the heating furnace 10 is increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The coal feeding amount of the coal mill 3 is gradually increased until it reaches 100 tons / hour. In the process of increasing the coal feeding amount of the coal mill 3, the load of the heating furnace 10 is simultaneously increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 126°C. The water evaporated from the coal is converted into steam and heated to become superheated steam, which gradually replaces the starting gas, so that the circulating medium transitions to superheated steam as the main medium. The amount of starting gas introduced is gradually reduced at a rate of 5% / hour. After about 20 hours, the introduction of starting gas is completely stopped, and the coal mill drying system enters a normal operating state. Under normal operating conditions, the superheated steam content in the exhaust gas is 80.57vol%, and the circulating gas flow rate entering the coal mill is 222.2 tons / hour (equivalent to 2.67kg circulating medium / 1.0kg dry coal powder) and the temperature is 275°C.

[0085] The circulating medium enters the coal mill 3 and blows the coal powder into the coal powder collector 4.

[0086] During the coal grinding and blowing process, the circulating medium heats the coal powder, converting the moisture it contains into gaseous state and entering the circulating medium. The temperature of the circulating medium leaving the coal mill 3 is 126°C, and the superheat is 33°C. A filter is arranged in the coal powder collector 4. After the circulating medium passes through the filter and leaves the coal powder collector 4, most of it (90.58%) enters the circulating fan 6, and the remaining part leaves the coal grinding drying system as the exhaust gas. 83.33 tons / hour of dry coal powder containing 4wt% of water is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 for boosting, it enters the heating furnace 10 for heating. The power of the circulating fan 6 is 1886kW, and the heat load of the heating furnace 10 is 11.93Gcal / hour. Considering the thermal efficiency of the heating furnace of 90%, 13.26Gcal / hour of fuel gas is required. If natural gas is used as fuel, 1550Nm of natural gas is required. 3 / h. The circulating medium heated by the heating furnace 10 enters the coal mill 3 again at a temperature of 275°C, completing a cycle.

[0087] Considering the inert gas entering the system due to equipment and process reasons, 5000Nm 3 / h, after calculation, the exhaust gas is 23.1 tons / hour. The specific exhaust gas data are shown in Table 4 below.

[0088] Table 4 Composition and flow rate of exhaust gas

[0089] Components Volume composition, vol% <![CDATA[Volume flow rate, Nm 3 / h]]> Mass composition, mass% Mass flow, kg / h <![CDATA[H2O]]> 80.57 20735 72.14 16666 <![CDATA[N2]]> 15.35 3950 21.37 4937 <![CDATA[O2]]> 4.08 1050 6.49 1499 <![CDATA[CO2]]> 0.00 0 0.00 0 total 100.00 25735 100.00 23102

[0090] As shown in Table 4 above, after the application of the utility model system, the water content in the exhaust gas is as high as 80.57 vol%, which is more than double the water content of the conventional system (36.20 vol%). The high water content in the exhaust gas reduces the difficulty of heat recovery and water resource recovery in the subsequent process; the exhaust gas is 23.1 tons / hour, which is equivalent to one-third of the exhaust gas volume of the conventional system (73.09 tons / hour), which reduces the investment in heat recovery and water resource recovery in the subsequent process, and also reduces waste gas emissions to protect the environment. The above data is based on 5000Nm 3 / h inert gas entering the system. If the inert gas entering the system is further reduced, the water content in the exhaust gas will further increase and the flow rate of the exhaust gas will further decrease.

[0091] Example 4: Hot air furnace heating device

[0092] In this embodiment 4, a hot air furnace is used to dry 100 tons / hour of wet coal containing 20 wt% of water to a water content of 4 wt%. Figure 5 shown.

[0093] The circulating fan 6 of the coal mill drying system is started, and the starting gas nitrogen is introduced at the outlet of the circulating fan 6. The gas in the system and the introduced starting gas are circulated under the action of the circulating fan 6. In order to stabilize the inlet pressure of the circulating fan 6 at 3kPaG, part of the circulating gas is discharged from the system at the inlet of the circulating fan 6. When the oxygen content of the circulating gas in the system is lower than 8vol%, the hot blast furnace 11 is started to heat the circulating gas. When the temperature of the circulating gas at the outlet of the coal mill 3 reaches 116℃, the wet coal with a water content of 20wt% enters the coal mill 3 from the coal bunker 1 through the weighing coal feeder 2.

[0094] The coal is ground into coal powder with the particle size meeting the requirements in the coal mill 3.

[0095] After coal is fed into the coal mill 3, the temperature of the circulating gas at the outlet of the coal mill 3 will decrease due to the evaporation of the water in the coal. The load of the hot blast furnace 11 is increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 116°C. The coal feeding amount of the coal mill 3 is gradually increased until it reaches 100 tons / hour. In the process of increasing the coal feeding amount of the coal mill 3, the load of the hot blast furnace 11 is simultaneously increased to keep the circulating gas temperature at the outlet of the coal mill 3 at 116°C. The water evaporated from the coal is converted into steam and heated to become superheated steam, which gradually replaces the starting gas, so that the circulating medium transitions to superheated steam as the main medium. The amount of starting gas introduced is gradually reduced at a rate of 5% / hour. After about 20 hours, the introduction of starting gas is completely stopped, and the coal mill drying system enters a normal operating state. Under normal operating conditions, the superheated steam content in the exhaust gas is 53.01vol%, and the circulating gas flow rate entering the coal mill is 222.2 tons / hour (equivalent to 2.67kg circulating medium / 1.0kg dry coal powder) and the temperature is 293°C.

[0096] The circulating medium enters the coal mill 3 and blows the coal powder into the coal powder collector 4.

[0097] During the coal grinding and blowing process, the circulating medium heats the coal powder, converting the moisture it contains into gaseous state and entering the circulating medium. The temperature of the circulating medium leaving the coal mill 3 is 116°C, and the superheat is 33°C. A filter is set in the coal powder collector 4. After the circulating medium passes through the filter and leaves the coal powder collector 4, most of it (81.03%) enters the circulating fan 6, and the remaining part leaves the coal grinding drying system as exhaust gas. 83.33 tons / hour of dry coal powder containing 4wt% of water is filtered and collected at the bottom of the coal powder collector 4, and then enters the subsequent process through the screw conveyor 5. After the circulating medium enters the circulating fan 6 for boosting, it enters the hot blast furnace 11 for heating. The power of the circulating fan 6 is 1583kW, and the heat load of the hot blast furnace 11 is 12.40Gcal / hour. Considering the thermal efficiency of the hot blast furnace of 90%, 13.78Gcal / hour of fuel gas is required. If natural gas is used as fuel, 1611Nm of natural gas is required. 3 / h. The circulating medium heated by the hot blast furnace 11 enters the coal mill 3 again at a temperature of 293°C, completing a cycle.

[0098] The combustion of natural gas produces 18850Nm flue gas 3 / h, all flue gas enters the circulating medium, and 5000Nm of inert gas enters the system due to equipment and process reasons 3 / h, after calculation, the exhaust gas is 46.5 tons / hour. The specific exhaust gas data are shown in Table 5 below.

[0099] Table 5 Composition and flow rate of exhaust gas

[0100] Components Volume composition, vol% <![CDATA[Volumetric flow rate, Nm 3 / h]]> Mass composition, mass% Mass flow, kg / h <![CDATA[H2O]]> 53.01 23636 40.82 18998 <![CDATA[N2]]> 39.69 17696 47.53 22117 <![CDATA[O2]]> 4.05 1804 5.53 2575 <![CDATA[CO2]]> 3.25 1450 6.12 2847 total 100.00 44586 100.00 46537

[0101] It can be seen from Table 5 above that after the application of the utility model system, the water content in the exhaust gas is as high as 53.01vol%, which is more than 40% higher than the water content of the conventional system (36.20vol%). The high water content in the exhaust gas reduces the difficulty of heat recovery and water resource recovery in the subsequent process; the exhaust gas is 46.5 tons / hour, which is equivalent to 64% of the exhaust gas volume of the conventional system (73.09 tons / hour), which reduces the investment in heat recovery and water resource recovery in the subsequent process, and also reduces waste gas emissions to protect the environment. The above data is based on 5000Nm 3 / h inert gas entering the system. If the inert gas entering the system is further reduced, the water content in the exhaust gas will further increase and the flow rate of the exhaust gas will further decrease.

[0102] The embodiments described above are only descriptions of the preferred implementation modes of the present utility model, and are not intended to limit the protection scope of the present utility model. Without departing from the design spirit of the present utility model, various modifications and improvements made to the technical solutions of the present utility model by ordinary technicians in this field should fall within the protection scope of the claims of the present utility model.

Claims

1. A coal grinding and drying system using superheated steam as a circulating medium, characterized in that: The coal grinding and drying system comprises a coal bunker (1), a weighing coal feeder (2), a coal grinding machine (3), a coal powder collector (4), a circulating fan (6), a heating device (7) and the coal grinding machine (3) which are connected in sequence; An outlet for exhaust gas is provided in a pipeline connecting the coal powder collector (4) and the circulating fan (6), and a starting gas inlet is provided in a pipeline connecting the heating device (7) and the circulating fan (6). When the coal grinding and drying system operates normally, the starting gas inlet is in a completely closed state.

2. The system according to claim 1, characterized in that The heating device is selected from any one or a combination of the following: (1) an electric heater (8), that is, the circulating medium enters the electric heater (8), and the electric heater (8) consumes electric energy to release heat to heat the circulating medium; (2) a steam heater (9), that is, the circulating medium enters the steam heater (9), and the steam in the steam heater releases heat to heat the circulating medium; (3) a heating furnace (10), that is, the circulating medium enters the coil in the heating furnace (10), and the fuel gas burns outside the coil in the heating furnace (10) to release heat to heat the circulating medium in the coil; (4) A hot blast furnace (11), that is, the circulating medium enters the hot blast furnace (11), the fuel gas burns in the hot blast furnace (11), and high-temperature flue gas is generated. The high-temperature flue gas is mixed with the circulating medium entering the hot blast furnace (11), thereby increasing the temperature of the circulating medium.

3. The system according to claim 1, characterized in that The coal grinding and drying system is a closed system.

4. The system according to claim 1, characterized in that The coal grinding and drying system is a system into which a starting gas is introduced during startup and before normal operation, and the starting gas is selected from one of nitrogen and carbon dioxide, or a mixture of the two.

5. The system according to claim 1, characterized in that When the coal grinding and drying system is started and operated, the pressure at the inlet of the circulating fan is 0.001 kPaG to 30 kPaG.

6. The system according to claim 1, characterized in that When the coal grinding and drying system operates normally, the superheated steam content in the circulating gas is higher than 50 vol%.

7. The system according to claim 1, characterized in that The sealing gas of the coal mill is superheated steam.

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