NO151071B - PROCEDURE FOR TEMPERATURE REGULATION OF EXOTHERMIC REACTIONS BY OVERHEATING OF WATER STEAM - Google Patents

Description

The invention relates to a method for temperature regulation of exothermic reactions by means of water vapor superheating, the water vapor being passed in several stages in a forced passage between the heat feeder and the reaction room.

In a common method for removing chemical pressure heat in so-called de-heating boilers, if evaporators are arranged in the reaction room or the subsequent product paths, a limit has been set for when an exact observation of certain temperatures is required in the event of simultaneous strong fluctuations in the heat generation, or when the evaporation temperatures are below the dew point of corrosive media.

The method according to the invention is generally suitable for such processes and enables very accurate temperature regulation. Thus, e.g. the strongly exothermic conversion of methanol to hydrocarbons in a fluidized bed is well temperature-regulated with the method according to the invention.

A further example of the joint performance

of such complicating conditions is the sulphating roasting of sulphidic ores, where the Cu and Zn sulphides present in the mixed concentrates must be transferred into soluble sulphates, where any pyrite, on the other hand, must be transferred into insoluble Fe20^, for which precise temperature control is necessary depending on the nature of the concentrate in

advised at 620 - 670°C. With changing concentrate composition, the heat to be removed is fluctuating. If water introduced with the blast furnace air and the residual moisture of the ore and the SO^ partial pressure required for sulphation are present, sulfuric acid dew points of up to 300°C appear.

Similar corrosive conditions prevail in the wet catalytic contacting of SC^-containing gases.

Even under non-corrosive conditions, such as in the case of catalysis of dry SC^-containing gases in a fluidized bed, an evaporator as a control heating surface is not suitable, above all when, as in processing plants, the concentration or quantity is fluctuating. The method according to the invention is particularly suitable for temperature control

ing of catalytic reactions, especially of the SC^ catalysis of

to SO^ in fluidized bed. By vortex bed is understood as well as a vortex bed without or with an outlet, respectively circulation of the vortex mass.

According to the invention, the requirements under the aforementioned conditions are met by making available steam of a corresponding temperature as a cooling medium. This cooling steam without the arrangement of an evaporator in the reaction room or in the production path is the only source of heat for the process in question, however, to produce it from own process heat is the task at hand.

The object of the invention is therefore a method for temperature regulation of exothermic reactions by superheating water vapour, the method being characterized in that water vapor is taken as a cooling medium from a direct pressure heat accumulator separated from the reaction room, arranged with boiling water filled with boiling water, fed in forced circulation in several rows in the reaction room, superheated where and each time it is then re-cooled in the heat accumulator by indirect evaporative cooling, the water vapor being kept at the same pressure in the heat accumulator and the number of superheating and re-cooling rows is chosen such that the ratio between the sum of the enthalpy differences of the re-cooling stages and the enthalpy difference between saturation steam and added feed water is kept at at least 1.1.

The proposed system consists of superheating heating surfaces arranged in the reaction space or the product paths and an indirectly charged direct pressure heat accumulator arranged outside the reaction space or the product path as shown in fig. 1.

Here means:

1 entry of reaction gas

2 fluidized bed reactor

3 exit of reaction gas

4 heat stores

5 supply of cooling steam

6 temperature probes

7 temperature control valve

8 superheating stages in a fluidized bed

9 cooling stages in thermal stores

10 drinking water supply to heat storage

11 position control valve for feed water

12 pressure control valve

13 removal of excess steam

14 mixers

15 temperature control valve

16 bypass wire

17 diversion for cooling steam

18 mixers

19 connecting line between mixers 18 and 14

20 line to the steam network

The mode of operation is as follows:

From the heat accumulator 4, saturation steam is withdrawn via line 5 regulated by temperature sensor 6 and valve 7 and superheated in several rows each time in one of the superheating stages 8 arranged in the fluid bed 2, at least 4, preferably 6-12, especially preferably 8-10, and is then cooled back in one of the cooling stages 9 arranged in the heat accumulator 4.

Equilibrium between that from the accumulator 4 in form

of saturated steam for cooling the fluidized bed heat extracted and the heat returned indirectly to the heat cooling stage 9 in the accumulator 4 is then present when the sum of the enthalpy difference of the steam cooled back in the recooling stage 9 is equal to the enthalpy difference between the feed water supplied via line 10 and that via line 5 exhaust steam.

According to the invention, this equilibrium is set independently of the given or selected steam conditions over the number of superheating and recooling rows.

Regarding the number of superheating and recooling rows, however, it is also possible to set other ratios greater than 1 if desired. With this precaution according to the invention, more steam is always produced in the heat accumulator 4 than

it is withdrawn from it for cooling purposes.

The greater the ratio of the sum of the enthalpy difference of the steam cooled in the recooling step to the enthalpy difference between steam and feed water is chosen, the more elastic the system reacts to fluctuating amounts of heat to be removed.

The excess steam not required for cooling is released via line 13, pressure-regulated through valve 12.

In order to keep the useful steam emitted via line 20 at the desired degree of heating, part of the amount of steam used for cooling the fluidized bed is heated after the last of the recooling stages 9, temperature regulated by means of valve 15 in the last of the superheating stages 8 so that after joining the lines 16 and 17 in the mixer 18 and continued via line 19 by bringing together the cooling steam with the excess saturated steam, the desired state emerges.

The vapor states passing in the above manner are shown in fig., lb.

Here means:

tw = intake water temperature

ts = saturation vapor temperature

tii = superheat temperature

tk = temperature of the vortex layer

tD = temperature after the last superheating step tA = temperature of released useful steam

i = enthalpy at the possible temperatures.

The diagram also clearly shows that by choosing the number of superheating and recooling rows, the temperature range of the steam used for cooling can be chosen as desired.

In particular, with a small enthalpy difference in the steps, a corresponding increase in the number of steps makes it possible to achieve a more extensive thermostatization of the reaction process.

In fig. 2, the numbers have the following meaning:

21 whirlwind voices

22 intakes

2 3 outlets

24 voice air entry

2 5 accumulator

26 wire

2 7 temperature sensor

2 8 valve

29 heat exchanger

30 overheating stages

31 cooling stages

32 wire

33 valve

34 valve

35 wire

36 wire

37 mixes

38 valve

39 wire

40 mixers

41 wire

42 outlets.

When cooling corrosive media, the steam used for cooling according to fig. 2 before entering the first superheating stage in the indirect heat exchanger 29 to a temperature outside the corrosive area.

The heater's operational readiness can be produced

in a simple way, e.g. by blowing in mains steam, if this is available. If this is not present, the first charging takes place using a circulation evaporator not shown in the figure during the heating process with the same hot gases with which the fluidized bed is brought to working temperature.

The working method and the system according to the invention for the temperature control shall be explained in more detail in the following examples of a SO^ vortex catalysis and a sulphating roasting.

Example 1

According to fig. let trees 30,000 m<3> (referenced

to the normal state of 0°C and 1.013 bar) per hour with approx.

14% by volume SO2 and 10% by volume 02 with a temperature of 380°C over line 1 into a fluidized bed 2 of catalyst mass.

The temperature a<y> of the reaction gas exiting over line 3 is 480°C. The catalytic conversion to SO^ is 9 3% and, after removal of losses during cooling, the heat carrying away is 13.12 • IO<6>kJ/h.

To remove this heat, 4511 kg of saturated steam of 35 bar and 241.4°C corresponding to an enthalpy of 2803 kJ/kg is taken from the heat accumulator 4 via line 5 regulated by temperature sensor 6 and valve 7 and heated in the first superheating stage 8 to 440° C, corresponding to an enthalpy of 3316 kJ/kg.

The steam is then cooled back in the first off

the cooling stages 9 to 2 75°C arranged in the heat accumulator 4 correspond to an enthalpy of 29 31 kJOkg.

The enthalpy difference of 385 kJ/kg specified in the heat accumulator 4 corresponds to the amount of steam of 4,511 kg/hour the necessary heat for preheating and evaporation of 716 kg/hour feed water, which is supplied at 90°C via line 1, level-regulated by valve 11 to the heat store 4.

In forced flow, the same quantity of steam of 4511 kg/hour then passes in 6 further rows one after the other each time in one of the superheating stages 8 and one of the recooling stages 9, the steam each time being heated to 275°C corresponding to an enthalpy of 2931 kJOkg to 440°C , corresponding to an enthalpy of 3316 kJ/kg and then cooled back to the state of 275°C.

At each of these recooling stages 9, a further 716 kg/hour of feed water of 90°C is preheated and evaporated to boiling temperature.

That is, in summary, in accumulator 4, 4511 kg/hour of superheated steam from the combined 7 stages, 5013 kg/hour of saturated steam of 35 bar and 241°C are cooled back

of a feed water of 90°C is produced.

The ratio of the total amount of steam produced

until the amount of steam used for cooling the vortex layer 2 amounts to 1.1.1, i.e. an 11% control reserve is present.

The amount of steam of 502 kg/hour not required for cooling the fluidized bed is supplied as saturated steam, pressure-regulated by means of valve 12 via line 13 to the mixer 14.

In order to keep the steam produced in an amount of 5013 kg/hour at a state of 300°C corresponding to an enthalpy of 2997 kJOkg, a part of the amount of steam used for catalyst cooling is heated after the last in this case, the seventh stage of the recooling stages in temperature-controlled valve 15 in a further, in this case, eighth stage of the over-heating stage 8 so that after connecting the lines 16 and 17 behind the mixer 18, a temperature of 309°C is obtained corresponding to an enthalpy of 3020 kJOkg.

This steam is combined via line 19 in the mixer

14 with the 502 kg/

hour saturated steam, so that" above line 20 5013 emerges

kg/hour of steam at 30 bar 300°C, corresponding to an enthalpy of

299 7 kJ/kg.

Example 2

According to fig. 2 is introduced into a vortex shaker 21 above the intake 22 approx. 10.5 tonnes/hour of a concentrate of sulphidic Cu, Zn and Fe minerals and the roasting material is removed at 23.

With the aid of the roasting process, the amount of Fe must be transferred into insoluble Fe20^, the amount of Cu and Zn, on the other hand, into soluble

lig sulfates. This selective process requires a precise regulation of the temperature in this case at 650°C.

The one with the humidity of the at 24 entering voice air of 24,000 m<3> (in normal condition referred to 1.013

bar and 0°C) per hour, as well as of the residual moisture of the total amount of water brought in by 22 entering concentrate

amounts to 1 tonne/hour, whereby the required SOg partial pressure for sulphation results in a sulfuric acid dew point of approx. 250°C.

The heat released by this process of 32.7 •

IO<6> kJ/hour is removed as follows: From the accumulator 25 is withdrawn via line 26 regulated by temperature sensor 27 and valve 28

8000 kg/hour saturated steam of 35 bar and 241°C corresponding to an enthalpy of 2 80 3 kJOkg. Because the temperature of this steam is below the sulfuric acid dew point, it is preheated to avoid corrosion before entering the first of the superheating stages 30 in heat exchanger 29 to 280°C before it is heated to 500°C corresponding to an enthalpy of 3453 kJ/kg.

After emitting an enthalpy difference of 141

kJ/kg to the saturated steam flowing countercurrently in the heat exchanger 29, the steam stream enters the first of the recooling stages 31 arranged in the storage 25 where it is cooled during preheating and evaporation of 1215 kg/hour of it at 90°C over a line 32, level regulated by means of valve 33 incoming feed water to 280°C corresponding to an enthalpy of 2944 kJ/kg.

In further forced passage is then passed

of the same amount of steam of 8000 kg/hour in six further rows each time in one of the superheating stages 30 and one of the recooling stages 31, the steam each time being heated from 280°C corresponding to an enthalpy of 2944 kJOkg to 500^C corresponding to an enthalpy of 3453 kJOkg and then back-cooled to the state of 280°C.

With the aid of the enthalpy difference of 509 kJ/kg produced in each of the recooling steps 31, a steam flow of 8000 kg/hour is preheated and evaporated each time a further 1679 kg/hour of feed water of 90°C to the boiling temperature of 241°C.

After passing through the last of the altogether 8 superheating stages 30 and heating to 500°C, part of the amount of steam is recooled, temperature regulated by means of a valve 34 in the last of the altogether 8 recooling stages so that after connecting the lines 35 and 36 it sets behind the mixer 37 a temperature of 350°C corresponding to an enthalpy of 3112 kJOkg.

By giving an enthalpy difference of 341 kJ/kg, preheated and vaporized at 8000 kg/h in the last / of the total 8 recooling stages 31 the remaining 1,188.8 kg/h of the total 12,476 kg/h of that with 90°C via line 32 into the storage 5 incoming feed water to the boiling temperature of 241.4°C.

The saturated steam quantity of 4,476 kg/hour not required for cooling the vortex roaster 21 is pressure-regulated by means of valve 38 via line 39 in the mixer 40 with the steam flow of 350°C coming from the mixer 37, so that it is removed via line 41 12 4 76 kg/hour of steam at 300°C corresponding to an enthalpy of 2994 kJ/kg at 42.

The ratio has produced a total amount of steam until the amount of steam required for cooling the vortex roaster 31 amounts to 1.56, with which a sufficient regulation reserve has been provided for sudden load overruns.

When processing the same amount of concentrate according to the hitherto usual methods with temperature control by direct water input of approx. 10.5 tonnes/hour, at 42 outgoing flue gas volume would increase from 21,000 to approx. 33,000 m 3,^/hour,. whereby, in addition to energy loss as a further disadvantage, it also had to be taken with an increase in the cross-section of the vortex shaker 21 in relation to the method according to the invention by around approx. 50%.

Claims (4)

1. Method for temperature control of exothermic reactions by superheating water vapour, characterized in that water vapor is taken as a cooling medium from a constant pressure heat accumulator arranged separately from the reaction space and filled with boiling water and is forced to pass through several rows in the reaction space, is superheated there and re-cooled each time thereafter in the heat accumulator by indirect evaporative cooling, as in the heat accumulator the water vapor is kept at the same pressure and the number of superheating and recooling rows is chosen so that the ratio between the sum of the enthalpy differences of the recooling stages and the enthalpy difference between saturated steam and added feed water is kept at at least 1.1. 2. Method according to claim 1, characterized in that the saturated steam withdrawn from the heat accumulator is preheated before entry into the first superheating stage by indirect heat exchange with the highly heated steam emerging from this or one of the other superheating stages. 3. Method according to claim 1 or 2, characterized in that the reaction space is designed for a fluidized bed. 4. Use of the method according to claims 1-3 for carrying out an exothermic catalytic SC>2 conversion process.