DE3432783A1 - Heat recovery from fossil fuel flue gases with simultaneous purification of the flue gases from sulphur oxides and nitrogen oxides and the generation of electrical power with the aid of the recovered thermal energy, and the production of mixed fertiliser from the sulphur oxides and nitrogen oxides - Google Patents

Abstract

The invention relates to a process for heat recovery from fossil fuel flue gases with simultaneous purification of the flue gases from sulphur oxides and nitrogen oxides and the generation of electrical power with the aid of the recovered thermal energy, such as are frequently encountered in combustion plants of steam generation plants in EVU's, the chemical industry, the cement industry etc., and which are fed with fossil fuels. This process unites in a harmonious manner energy saving and environmental protection, here restriction of emissions of sulphur oxides and nitrogen oxides. The flue gases are cooled and purified in a three-stage process. 1st stage: ORC plant; power generation. 2nd stage: intercooler; utility water having a temperature of 45 DEG C can be generated here. 3rd stage: refrigeration equipment; alternatively to the refrigeration equipment, the flue gas can also be cooled here using liquid nitrogen. The condensates from each stage are collected in a joint condensate vessel and are pumped around in a packed column. An ammonia/air mixture is injected in countercurrent so that formation of a mixed fertiliser occurs here.

Description

Heat recovery from the flue gases from fossil fuels

with simultaneous cleaning of the flue gases from the sulfur and nitrogen oxides and the generation of electricity with the help of recovered thermal energy, as well as the production of mixed fertilizers from sulfur oxides and nitrogen oxides.

Process description: A. Heat recovery and power generation The Flue gas flow coming from the furnace, i.e. after the electrostatic precipitator, has here A temperature of 1400 C is ideally used as an evaporator in heat-insulated ears directed.

The heat exchange takes place in the evaporator. As a coolant (primary Cycle) halogenated hydrocarbons are preferably used. she are able to generate the necessary pressures and thus a turbine and thus also to operate a generator profitably. The actually low content Flue gas is from these already mentioned 14U0 C, depending on the sulfur content of the burned Coal or fuel, these temperatures are also higher, at one temperature t e cooled.

The Clausius-Rankine process is ideally used as the thermal process. This process is also generally known as the ÜRC process (ürganic Rankine cycle). There is basically the [possibility of using this thermal process in wet steam, To operate in saturated steam or in overheated areas. It is most beneficial to this thermal process to operate in the overheated area, because here the thermal Efficiency is greatest.

The coolant itself in the circuit, that is, the liquid coolant with the initial temperature t, the entrained a heat energy of the flue gases absorbs and warms up to one Evaporation temperature te. It evaporates and is further superheated isobarically to an overheating temperature tü. It increases the pressure from the initial pressure Pa (pressure after the turbine outlet) to the final pressure Pe (Pressure before turbine inlet). The coolant, which is now vapor, now becomes isentropic expands in the turbine. The coolant cools down to the initial temperature t a and the pressure goes back to the initial pressure Pa. After the expansion The heat of evaporation is withdrawn isentropisobarically from coolant that is still vaporous and thus liquefied it again. The condensed coolant is by means of a Feed pump used again to cool the flue gas flow.

The cooling medium cycle is thus closed. With part of this Recovered thermal energy is carried out on the turbine for the cycle work t w.

The frequency of the generated electricity depends solely on which Generator is used.

8. Purification of the flue gases from the sulfur and nitrogen oxides. Cools a flue gas from a fossil fuel (hard coal, lignite, petroleum or Natural gas), then there is a point at which sulfur and nitrogen oxides condense out. This point is also called the acid dew point and the associated oil temperature the acid dew point temperature. The acid dew temperature is dependent on many factors addicted. But it is generally at 130 ° -180 L. If the flue gas is now on cooled to a certain temperature, then the sulfur oxides become YtJ - 95 «0 condensed out.

The sulfur tri oxj d condenses in the form of sulfuric acid and the sulfur dioxide in the form of sulphurous acid, The cooling off the flue gases take place in three stages. The condensates from each stage are in one common condensate collection. Because the reaction of nitric oxide to nitrogen dioxide is an exothermic reaction, the flue gas to relatively deep Temperatures is cooled and also a large excess of oxygen in the flue gas is, there is a further conversion of nitrogen monoxide to nitrogen dioxide. -The nitrogen dioxide is also condensed out in the form of nitric acid and converted into fed into the condensate collector. The condensates are generated from the condensate collector pumped into a packed column.

In countercurrent, ammonia is passed into the packed column, see above that there is a chemical reaction here: The end product of this chemical Reaction is a high quality SLicI <mixed material fertilizer of the form (NH4) 2SO4 @ 2 NH4NO3 C. Advantages of the procedure over other procedures 1. There is a much higher flue gas desulphurization than with other processes where the flue gases still contain up to 200 mg SO2 / Nm3 flue gas. With this one This process achieves a flue gas desulphurization of up to 100 - 150 mg m flue gas.

2. With other @ flue gas desulphurisation processes, additionally Energy consumed to achieve a reasonably acceptable flue gas desulphurization. With this process, energy is still recovered.

3. The efficiency of the combustion system is increased considerably.

4. This method is not only suitable for power plants in EVUS, but also in firing systems in the chemical industry, the cement industry, etc.

5. One achieves through the sale of the resulting end products additional profit.

6. This process also cleans the flue gases of the actually even more dangerous nitrogen oxides.

7. Because other processes (wet processes) do not produce plaster of paris you save yourself the e @ landfill.

8. If there is a risk of encrustation of system parts with other processes, which reduce the degree of desulphurization or put this part of the plant out of operation, there is no risk of incrustation with this process.

9. This flue gas cleaning system can also be retrofitted or in addition to an existing @ flue gas cleaning system 10. The consumption of resources is low, cheap and easy to obtain.

11. External energies such as water vapor, electricity etc. are omitted.

12. With this method, all system parts that are necessary for the corresponding regenerative wet or dry processes are required. This lowers the operating costs and system costs are considerable.

Calculations The calculations are made for a pilot plant with a Flue gas quantity of 120,000 Nm3 flue gas / h # 39 MW thermal output. at the combustion of coal becomes 5 (<j of sulfur z @ sulfur trioxide and 95 oxidized to sulfur dioxide. Since the sulfur content in the coal is 11 g S / kg coal = 1.1%, 0.55 g S becomes sulfur trioxide (SO2) and 10.45 g S becomes sulfur dioxide (SO2) oxidized.

Burning 1 kg of coal produces 10 Nm3 of flue gas.

SO = 80.07 g / mol SO2 = 64.07 g / mol S = 32.07 g / mol Thus: Furthermore, there are 600 mg NOx / Nm3 in the flue gas. Of this, 10% NO2 = 60 mg NO2 and 90% NO = 540 mg.

NO = 30.0 g / mole NO2 = 46.0 g / mole This results in the following flue gas @ us @ mmensionen-before entry into the ORC system: 1. Carbon dioxide (CO2) = 1.15288 Nm3 2. Sulfur dioxide (SO2) = 0.00077 Nm3 = 2088 mg 3. Sulfur trioxide (SO3) = 0.00003 Nm3 = 0.1373 g 4th nitrogen (N2 = 0.73195 Nm3 5th nitrogen monoxide (NU) = 0.00040 Nm3 = 540 mg 6th nitrogen dioxide (NU,) 3 0.00003 Nm3 = 60 mg 7. Oxygen (O2 = 0.03892 Nm3 8. Water vapor (H2O) = 0.06500 Nm3 13 = 52.233 g 0.98998 Nm3 Table 12 Specific heat for air and flue gases from solid fuels 1st stage: ORC process The amount of coolant circulating (Frigen 114) mr is mF = 130,000 kg / h. The filling quantity mF = 20,000 kg. The price for the generator is an additional DM 33,000 (according to a statement by lir. Kallwitz). The flue gas is cooled from 140 ° C to 50 ° C in this stage.

The operating volume for the flue gas in this stage results from: This means that in the flue gas: m @@ = 0.1373 g SO3 / 1.497 m3 -3 -V t140 1 120,000 Nm3 / h (1 + 140 @ = 181504.67 m3 / h -273.15 K The water vapor content is: w1 = 52.233 gH2O / 1.497 m3 One can assume a stoichiometric calculation for this process: H2SO4 = 98.07 g / Dlol This produces sulfuric acid: mH2SO4 = 0.168 g H2SO4 / 1.497 m3 1st stage: ORC process The consumption of water for this results in: The water vapor remains in the flue gas and thus goes: into the second stage: w2 = w1 - wH2O w2 = 52.233 g H2O / 1.497 m3 - 0.038 g H2O / 1.497 w2 = 52.194 g H20 1st stage: ORC process Another condensation of water vapor or sulfur oxides are not produced in this stage, since the actual absorption capacity in the flue gas at a temperature of 50 ° C is w = 83.0 g / m3. However, this value is considerably higher than the water vapor in the flue gas. All other data for this stage can be found in the offer letter.

2nd stage: Intercooler In the intercooler, the flue gas is at 50 ° C cooled to 25 ° C. The coolant is water.

The cooling water inlet temperature te = 15 ° C The cooling water outlet temperature ta = 35 ° C #t = 20 K The absorption capacity of water vapor in the flue gas at a Temperature of 25 ° C is w3 = 23.11 g I121) / m3 Vt50 = 1.183 m3 V = 141 966 m3 / h The partial pressure of the sulfur dioxide is PSO @ = 0.000789 bar.

@@ 2 The resulting mixture temperature of the condensate is with 50 ° C + 25 ° C tm = --------------- = 38 ° C assumed.

2 At tm = 38 ° C, the technical solubility is tsltoefficient for S02 in water and with = 2.92 g / Ncm3, as well as the partial pressure of SO2, the real solubility coefficient for SO2 in water is: # t1 = \ 48.38 mg SO2 / g (H2O) 2nd stage: Intercooler Water vapor condenses in this stage from: w4 = w2 - w3 w4 = 52.194 g H2O / 1.183 m3 - 23.0 g H2O / 1.183 m3 w4 = 29.194 g H2O / 1.183 m3 Thus, the following amount of sulfur dioxide condenses in this stage: 1KSO2 = # t1 Accordingly, the following amount of SO2 condenses here every hour: The following SO2 content still remains in the flue gas and thus goes into the third stage: m2SO2 = m1SO2 - m1KSO2 m2SO2 = 2088 mg SO2 / 1.183 m3 - 1412 mg SO2 / 1.183 m3 m2SO2 = 676 mg SO2 2nd stage: Intercooler Condensed on water vapor : The amount of heat to be dissipated is calculated as follows: cpm = 1.4 KJ / m3 # K #t = 50 ° C - 25 ° C = 25 K #hvmm = 2441.9 KJ / kg # K (averaged between 50 ° C and 25 ° C).

QK = 13523835.72 KJ / h cooling water requirement cw = 4.18 KJ / kg #K 3rd stage: refrigeration machine In the refrigeration machine, the last cleaning stage for the flue gas, the flue gas is cooled from 25 ° C to 5 ° C. The absorption capacity of water vapor in the flue gas at a temperature of 5 ° C is w5 = 6.3 g H20 / m3 3 Vt25 - 1,092 m 3 Vt25 = 130983.0 m Thus in this stage water condenses from: w6 = w3 - w5 w6 = 23.0 g / 1.002 m3 - 6.3 g / 1.092 m3 = 16.7 g / 12.092 m3 The resulting mixture temperature is 25 ° C + 5 ° C tm = ----------- ----- = 15 ° C assumed.

2 Since a large amount of sulfur dioxide and water vapor is already condensing out the partial pressure of the SO2 must be recalculated. There are still m2SO2 in the flue gas = 676 mg 502 = 0.0106 mol / m3; 3 Water vapor is still w3 = 23.0 9 = 1.28 mol / m3.

This results in a new nges. from nges. = 423.2078 mol / m3.

3 0.0106 mol # m3 XSO2 = --------------------- = 0.000251 42.2078 mol m3 PSO2 = 1.0133 bar # 0.0002541 = 0.000254 bar 3rd stage: refrigeration machine At tm = 15 ° C the technical solubility coefficient for SO2 in water is: and with i '= 2.92 g / Ncm3, as well as the new partial pressure, 45 Ncm3 SO2 # 2.92 g # 0.00025 bar # 1000 mg # t2 = -------------- ------------------------------------ g (H2O) # bar # Ncm3 # g # t2 = 33 , 4 mg SO2 / g H2O So here condenses on StJ2 from: The following amount of SO2 goes into the chimney with the flue gas: m3SO2 = M2SO2 - m2KSO2 m3SO2 = 676 mg SO2 / 1.092 m3 - 557.8 mg SO2 / 1.092 m3 m2SO2 = 118.2 mg SO2 The hourly amount of sulfur dioxide is therefore: m2KSO2 = m2KSO2 # vt25 3rd stage: refrigeration machine The amount of heat to be dissipated here is: # hvwm = 2465.5 KJ / kg (averaged between 25 ° C and 5 ° C) c @@ = 1.4 KJ / m³ # K pm #t = 25 ° C - 50C = 20 K 3 3 130983 m. 1.4 kJ. 20 1 <16.7 9. 130983 m³. 2465, '= / 3 + / 1.092 m³ h. m. K QK = 8606241 KJ / h 3rd stage: refrigeration machine 3432783 Frigen 22 is used as the coolant for the refrigeration machine :.

The evaporation temperature of the coolant is 0 ° C.

The coolant is compressed to a final pressure e = 10.411 bar; te = 25 ° C.

The initial pressure pa = 4.98 bar; ta # = 1.178 (from table) pa = 4.98 bar (from table) pe = 10.411 bar (from table Va = 0.04718 m³ / kg (from table) h1 = 404.93 KJ / kg (from table) C1 = 0.78 4.98 0.04718 # 1), 78 ad = - 102 = 0.001797 KW pad # 3600 KJ h2 = h1 + ------------------- 1 KW # h # mf 3rd stage: refrigeration machine 0.001797 KW # 3600 KJ # h h2 = 404.93 kJ / kg + h # KW kg h2 = 413.55 kJ / kg This results in the following enthalpies for this cooling circuit.

Enthalpies: h1 = 404.93 KJ / kg (from table) h2 = h .. = 413.55 kJ / kg (calculated) 2 u h2 = 412.30 kJ / kg (from table) h3 = h4 = 230.50 KJ / kg (from table) #hvf = 181.89 KJ / kg (from table) 4.98 0.04718 0.78 49340 ad = - 88.65 kW = 90 KW] 102 #pol = palytropic efficiency = 0.8 #m = mechanical efficiency = 0.97 - 0.99 = 0.98 3rd stage: refrigeration machine #mot = motor efficiency = 0.9 90 KW PMot = -------- ------------- = 127.6 KW = 130 KW 0.8 # 0.98 # 0.9 The amount of heat to be dissipated in the coolant condenser is: QCond. = QW = mF # (#hvF + (h2 - h2)) QCond. = 49340 kg / h (181.89 KJ / kg + (413.55 - 404.93) k3 / kg QCond. = 9399763.4 KJ / h 3rd stage: refrigeration machine Assuming that the coolant in the refrigeration machine can be circulated just as often as in the OR £ system, the following coolant fill quantity results here: N = circulations / h; N = 6 49349 kg # g mF = ----------------- = 8224 kg = 8300 kg 6 # h 3rd stage: refrigeration machine The flue gas can be subcooled with the cold flue gas flow.

This reduces the compressor's power requirement because the amount of coolant to be circulated is less. The filling quantity does not change as a result, as it must be taken into account that the coolant cannot be subcooled.

cF = 1.306 kJ / kg. K (heat atlas) 3 cpm = 1.4 KJ / m # K mF = 49340 kg / h vt5 = 122197 m3 / h Q3 = Q1 + Q2 - Q4 vt5 # cpm # #t = Q1 + Q2 -Q1 + Q23 - Q4 #t = -------------------- vt5 # cpm 3rd stage: refrigeration machine 122197 m3 # 1.4 KJ # 5 K 1 = ------- ---------------------- = 855379 KJ / hh # m3 # K 49340 kg 1.306 kJ 25 K = ------------ ------------------------- = 1610951 KJ / hh kg K 49340 kg # 1.306 KJ # 18 K Q4 = -------- ---------------------------- = 1159884.72 KJ / hh # kg # K #t = (855379 KJ / h + 1610951 KJ / h - 1159884.72 KJ / h) #h 3 122197 m. 1.4 kJ = 7.6 K = 8 K The flue gas is heated to 12 ° C. The operating volume of the flue gas is thus: The enthalpy of the coolant h3 = h4 is thus: h3 = h4 = 221.88 kJ / kg (from table) 4.98 # 0.04718 # 0.78 # 47016 pad = ---------------------------------- = 84.5 KW = 85 KW 102 85 KW pMot = ------------------- = 121 KW = 125 KW 0.8 # 0.98 # 0.9 3. Stage: As an alternative to the refrigeration machine, which consumes a large part of the energy generated by the URE system, the flue gas can also be cooled with liquid nitrogen in the third stage. This would have the following advantages: 1. There is a much larger amount of electricity available, which is generated by the RC system.

2. The system costs are reduced. Because that would only be here much cheaper to install WAT.

3. The heated nitrogen can simply be vented into the air.

4. An additional energy wall for the third stage is not necessary because the liquid nitrogen is under excess pressure and therefore by itself flows into the system.

5. It is easy to regulate, only via a valve. 3rd stage: Data for liquid nitrogen (heat atlas) cpN2 = 1.038 KJ / kg # K #t = 0 ° C - (- 195.7 ° C) = 195.7 K # hvN2 = = 201 kJ / kg vN2 s = 1.25 kg / l = 1250 kg / Nm3 3rd stage: Calculation of the desulphurisation level With a high degree of probability, the process can be expected to remove nitrogen oxides from the flue gases.

Especially since the; reaction: @ is an exothermic reaction and the flue gas has cooled down very deeply. furthermore the oxygen excess for this reaction is ic-fold than is necessary for this reaction. This means,.

according to the law of mass action, this reaction is from two sides positively influenced. On the other hand, you can also inject some ozone into the flue gas and thus accelerate this reaction.

The forming NO2 reacts with the water under the following reaction equations: to nitric acid, so that a mixture of dilute nitric acid, sulfuric acid and sulphurous acid is present in the condensate container. Since this mixture is not immediately discharged in the condensate container and therefore has a short dwell time and air can also be passed over this mixture, further reactions to nitric acid will occur. The sulphurous acid will also continue to react to form sulfuric acid.

This will result in a mixed fertilizer after the reaction in the full body column with the ammonia. Consists of ammonium sulfate and ammonium nitrate: (NH4.) 2So4 2 NH4NO3 consumption of ammonia If one assumes a complete conversion of the existing condensates, then the following reactions result: 1st stage: 2nd stage: In the first stage, sulfuric acid must be used as a starting point.

The condensates from the second and third stage can be combined will.

1st stage: 3 0.09807 kg H2504 = 0.0448 Nm N113 20.37 kg / h H2504 = X Nm3 / h NH3 2nd and 3rd stage: 0.12814 kg SO2 = 0.0896 Nm3 NH3 236.35 kg / h SO2 = x Nm3 / h NH3 24 nitric acid Fig. 11. Oxidation times of NO-air mixtures at 30 ° C depending on the initial NO content and the degree of conversion (according to HW Webb: Absorption of Nitrous Gases, Arnold k Co., London 1923, p. 23) Consumption of ammonia The ratio of oxygen to nitrogen monoxide in the flue gas is 99.0% = O2 1.0% = NO As the figure shows, the oxidation time with these ratios and an 80% conversion of NO to N112 is approx. 90 sel < Temperature of 30 ° C. This means that an 80% conversion of NO to NO is already achieved at the end of the second stage.

3 After this conversion, there are 500 my N112 / Nm3 in the flue gas.

46 g NO, = 63 g HN03 0.50 g NO2 / 1.183 m3 = X g HNO3 / 1.183 m3 mHNO3 = 0.64 g HNO3 / 1.183 m3 0.063 kg HN03 = 0.0224 Nm3 NH3 76.8 kg HNO3 / h = X Nm3 Nil3 / h Ammonia consumption Air requirement Based on equation (2): 0.12814 kg S02 = 0.0224 Nm3 O2 236.35 kg 502 / h = X Nm3 O2 / h End products Based on reaction equation (2) and 100% conversion results: 1st stage: 2nd and 3rd stage: 1 - 2: isentropic expansion of the coolant in the turbine 2 - 2 - 3: isothermal - isobaric - liquefaction of the medium vapor 3 - 4: isentropic compression of the condensate in the feed pump 4 - 5: preheating of the coolant to evaporation temperature 5 - 1: isothermal - Isobaric evaporation of the coolant in the evaporator data: h1 = 372.69 I <J / kg (from table; at 54 ° C) h2 = 359.00 KJ / kg (from diagram; at 540C) # hvF1 = 115.51 KJ / kg (from table; at 54 ° C) h5 = 257.18 kJ / kg (from table; at S4 ° C) h2 = 354.29 KJ / kg (from table; at 25 ° C) h3 = h4 = 225 , 70 KJ / kg (from table; at 25 ° C) # hvF2 = 128.59 KJ / kg (from table; at 250c) Pa = 2.151 bar (from table; at 25 ° C) Pe = 4.997 bar (from table ; at 54 ° C) Calculation of the cycle work ww = (h1 - h4) - (h2 - h3) w = (372.69 KJ / kg - 225.70 KJ / kg) - (359.00 KJ / kg - 225, 70 KJ / kg w = 13.69 KJ / kg calculation of the required amount of Friqen F total = QVorw. + QVerd.

QR = QR140 - QR50 QR = Qges Calculation of the internal performance Calculation of the amount of heat to be dissipated in the coolant condenser QK = 124583 kg / h # (128.59 KJ / kg + (359.00 KJ / kg - 354.29 KJ / kg QK = 16606914 KJ / kg Calculation of the clamping stress PKL = Pi ## m ## Gen ## i PKL = 473.76 KW # 0.98 # 0.98 # 0.84 = 382.2 KW Legend for the notification @@@@@@@ 1. Evaporator and superheater 2. Turbine and generator 3. Coolant condenser unit of the ORC system 4. Feed pump 5 - 8. Alkali scrubber with agitator 9. Dust separator 10. Chimney Legend for drawing 1. B. 1. Preheater and evaporator 2. Turbine and generator 3. Coolant condenser unit of the ORC system 4. Feed pump 6. Gas-liquid heat exchanger 8. Evaporator 9. Coolant compressor unit of the refrigeration machine 10. Coolant condenser 11. Expansion valve 5, 7, and 12. Cooling water pumps 13. Condensate collector 15. Filter, sieve 16. Acid mixing pump 17. Packing column 18. Fan 19. Chimney

Claims (5)

P a t e n t a n s p r ü c h e 1. Process for heat recovery from the smoke casings of fossil fuels with simultaneous cleaning of the smoke gases of the sulfur oxides (SO2 and SO3) and the nitrogen oxides (I \ U and NH2) and the production of electric current with the help of the recovered thermal energy, d a d u r c h e k e n n n n z e i c h n e t that the flue gas with a temperature of approx. ta = 140 ° C is cooled to a temperature le = 50 ° C. 2. The method according to claim 1, characterized in that for generating of electricity, preferably the ORC process (Irganic / Rankine Cycle Process ) anclewand becomes. The thermal process can be in wet steam - SaLt: dampf - or be done in the overheated area. Halogenated hydrocarbons can be used as coolants or other customary coolants, such as toluene, benzene, etc., can be used. 3. The method according to claim 1, characterized in that the flue gas in the first stage by falling below the acid dew point initially only the sulfur trioxide condensed in the form of sulfuric acid and stored in a common condensate collector, for all condensates that occur. 4. The method according to claim 1, characterized in that g e k e n nz e i c h n e t the breath gas is further cooled in a second and third stage and thus the water vapor dew point is also fallen below and there is a final cleaning The flue gas from the sulfur and nitrogen oxides takes place and enters the common condensate collector be directed. 5. The method according to claim 1, characterized in that the condensate mixture is pumped around in a packed column and in countercurrent an ammonia <- air - mixture is blown in, so that a mixed fertilizer is formed here :. 5. The method according to claim 1, characterized in that for the Further Cooling of the flue gas in the second stage in a liquid hot water exchanger is used and one for the third stage for further cooling of the flue gas Chiller. As an alternative to the refrigeration machine, the flue gas can also be mixed with liquid Nitrogen in a gas-gas heat exchanger.