FI81140B - Process for the treatment of combustible gas made from spent liquors from alkaline cellulose processes - Google Patents

Abstract

The invention relates to a process for the treatment of combustible gas that is produced from spent liquor from alkaline cellulose processes, especially from sulphate boiling, and which is suitable for energy production. In the process the combustible gas is brought into contact with certain calcium compounds at high temperature, there being a significant reduction in the quantity of sulphur constituents in the gas and, to a certain extent, calcining of the calcium carbonate necessary for recovery of the boiling chemicals. Conversion of the sulphur that is removed from the gas to active boiling chemical occurs in conjunction with normal causticizing.

Description

81 1 40 A process for the treatment of flue gas produced from the processing of ALKALINE CELLULOSE PROCESSES - 5 CaO), calcium carbonate (CaCOa) and calcium sulphide (CaS) at high temperature, which at the same time substantially reduces the amount of sulfur components in the gas, mainly hydrogen sulphide (H = S) and to a certain extent the calcium carbonate calcination required for regeneration of cooking chemicals. to the cooking chemical, sodium sulfide (Na * S), occurs during normal causticization.

The dry matter of the waste liquor (so-called black liquor) 20 produced in sulphate cooking consists mainly of three concentrations I. almost equal fraction of matter: inorganic compounds, lignin degradation products and carbohydrate degradation products (Alen, R., Chemistry 15 (1988) 565). In the conventional process for recovering sulphate black liquor 25, the extractants are first separated from the broth: as a raw soup, after which it is concentrated to a dry matter content of 65-75% and incinerated in a recovery boiler 2,81140 (Virkola, N.-E. (ed.), Wood pulp production, part 1, 2). edition, Academy of Technical Sciences, Turku 1983). In this case, the organic matter of the lye is converted into energy and the inorganic matter leaves the boiler mainly in the form of a melt, which consists primarily of sodium carbonate (Na 2 CO 4), sodium sulfide (Na * S) and sodium sulfate (Na 2 SCU). These salts are returned to the cooking through a causticization step in which NaaaCO is converted to the active cooking chemical, sodium hydroxide (NaOH), by means of calcium hydroxide (Ca (OH) 2):

CaO + HaO - »Ca (OH) a (1)

Ca (OH) a + NaaCOa -> CaCOa + 2NaOH (2)

The required CaO is in turn regenerated by separately calcining the CaCOa formed in reaction (2) in the so-called in a mesa-15 oven according to the following reaction:

CaCOa - »CaO + C02 (3)

Although it is reasonable to argue that in the current recovery process, the components of the black liquor are fully utilized, the recovery process 20 can nevertheless be substantially improved. With the exception of extractants, black-liquor organic matter is converted exclusively into energy, the majority of which is obtained as thermal energy, with a correspondingly small proportion of electrical energy. The thermal efficiency of the current boiler process (based on the upper 25 calorific values) is only 50-55%, taking into account the heat required to evaporate the waste liquor.

The art intake equipment for the sulphate process is also expensive, accounting for about AO% of the plant's total investment, and its operation involves a risk of meltwater explosion. For the reasons mentioned above, research has focused in part on the application of alternative conversion techniques to black liquor.

3,81140

Gasification technology offers an alternative in order to make more efficient use of black liquor. In gasification, the organic material of the raw material reacts with oxygen and water vapor at a high temperature, type 11 800 to 1300 5 ° C, and is converted into a gas with a calorific value. In particular, pressurized gasification technology coupled to a combined gas and steam turbine power plant (so-called gasification combined heat and power plant or KKV plant) has been of interest (Kohl, A.L., Can. J. Chem. Eng. 64 (1986) -10299). Figure 1 shows a simplified process diagram of a type of SME facility. Since the combustion gas produced from the raw material is burned in a gas turbine, the combustion gas must be quite clean and contain only very little solids as well as early metal-15 compounds (Mojtahedi, W., Chemistry 14 (1987) 835). The concentration of sulfur compounds must also be quite low, especially due to environmental emissions. For these reasons, the raw gas from the pressurized conversion reactor usually has to be purified and in the KKV solution this purification is performed / 20 specifically under pressure. In addition, the temperature of the treatment treatment is of great importance for the overall economy of the KKV process, where the general rule is that raising the temperature up to a certain limit contributes to the economy of the process.

25 In developing the method presented in this context, there are; . two new and surprising observations have been made, namely that the removal of the sulfur components of the combustion gas produced from the black liquor at high temperature and the calcination of CaCO »can be combined with the fact that the removal from the gas! The sulfur can then be converted to the active cooking chemical (Na * S) during normal causticization.

4,81140

The main features of the process according to the invention, which are set out in more detail in the claims, are: 1. In gas treatment, the fuel gas produced from the waste liquor is contacted with calcium compounds, mainly CaO, CaCOa and CaS.

2. A relatively high temperature is used in the gas treatment: 600 to 1300 ° C, whereby reactions (3) and (4) take place to a significant extent:

CaCOa -> CaO + COa (3) 10 CaO + HaS -> CaS + HaO (4)

The equilibrium states of these reactions as a function of temperature are shown in Figures 2 and 3. In the conventional chemical recovery process, the calcination reaction (3) is carried out exclusively in a separate lime kiln. Reaction (4) substantially reduces the hydrogen sulfide content of the gas to be treated.

3. In addition to the normal causticization reactions (1) and (2), reaction (5) takes place during the causticization step:

CaO «»> + HeO <i »- * Ca (OH) a <-.> (1)

Ca (OH) 2 t.q) + NäzCOa— * CaCOa («> + 2NaOH <« ^> (2) 20 CaS <»> + NaaCOscM) -4 CaCOa (»> + Na ^ S <««> (5)

The Gibbs energies (ΔΘ »» · κ) of reactions (1), (2) and (5) are -7 kcal / mol, -11 kcal / mol and -8 kcal / mol, respectively. Reaction (5) can also be carried out in a partially separate apparatus from reactions (1) and (2). The active cooking chemicals formed in reactions (2) 25 and (5), NaOH and Na 2 S, are recycled back to the cellulose cooking step, while the CaCOa formed in the same reactions is recycled back to the gas treatment step. In the most common embodiment of the process, the Na * COa present in reactions (2) and (5) is derived from that process step (so - called.

il s 81140 from the gasification stage) in which the fuel gas to be treated is produced from the waste liquor.

By integrating the process according to the invention into a gasification combined power plant (KKV plant) based on the gasification of waste liquor, considerable advantages are obtained compared to the traditional chemical and energy art extraction process, the extent of which, however, depends on the chosen embodiment: 1. The SME solution already offers many advantages. the soda recovery unit.

One of the most significant is the higher electricity / heat ratio in energy production made possible by the method. In this respect, the benefits increase up to a certain limit as a function of the increase in gas purification temperature. Since the method presented in this connection uses a relatively high temperature, 600-1300 ° C, the method is thus quite well suited as part of a KKV solution.

: 2. Since in the KKV solution the conversion of the effluent is carried out at elevated pressure, it makes technical sense to pressurize y; At the same time, there are other process steps involved in the chemical cycle, such as dissolution of inorganic salts, causticization and separation of lime (CaCO »). This results in significant cost and energy savings in the chemical cycle.

25 3. The method also brings improvements to the calcination stage, especially in the case where most of the total CaCOa generated in the plant is calcined in the gas treatment stage. The combined calcination-gas treatment reactor is a more cost-effective equipment solution than a conventional lime kiln. This process step does not require external fuel like a lime kiln, as it is able to partially utilize the thermal energy contained in the waste liquor components.

The gasification stage can be easily and advantageously combined with a secondary gasification stage, whereby it is possible to use the most optimized process conditions in the primary gasification stage than can reasonably be applied in connection with a single-stage gasification process. For example, the primary step 10 can be performed at a relatively low temperature, 600-750 ° C, to allow the inorganic compounds to remain in the solid phase. Primary gasification can therefore be carried out e.g. a fluidized bed reactor. The two-stage gasification process can also reduce the formation of an early metal aerosol compared to the one-stage process.

If necessary, the gas treatment step can be carried out in the same set of equipment as the primary gasification step of the waste liquor, for example by using a reactor in which two different fluidized beds are superimposed.

The following examples show four method-implementation options. These examples are intended to illustrate the invention without limiting it in any way. Furthermore, it is obvious to the person skilled in the art that the method is applicable to the recovery of waste broths (as well as those formed during cooking) generated by the temporal delignification processes of different types of raw materials. The method can also be applied to the treatment of gases other than combustion applications, such as synthesis gases.

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Example l

Figure A shows a simplified process diagram of an implementation alternative according to the example. The concentrated sulphate waste liquor (substance stream 1) is gasified with air or oxygen (substance stream 2) and possibly with water vapor in a fluidized bed reactor I at a temperature of 600 to 900 ° C and a pressure of 1 to 3 MPa. The fluidized bed material consists mainly of inorganic salts derived from the broth, mainly Na 2 CO 3. As a possible additive, it is possible to use a material taken from 1 cycle (material stream 7), the purpose of which is both to improve the fluidizing properties of the bed and to maintain a temperature somewhat higher than the melting point of the sodium salts. Sulfur leaves the reactor mainly as sulfur-15 bound to hydrogen in the gas phase (stream 3). In addition, e.g. organosulfur compounds (chemically primarily mercaptans and sulfides) and inorganic sodium sulfide.

In the second fluidized bed reactor II, secondary gasification and gas treatment according to the invention are carried out. The fluidized bed material in this case consists mainly of calcium compounds (CaO, CaCOa and CaS). In addition, there are sodium compounds present in the feed streams (material streams 3 and A), which promote the merlo-25 merification of calcium particles into particles of suitable size. The temperature is maintained in the range of 800 to 1100 ° C and the pressure is 1 to 3 MPa. Partially unreacted materials in the primary gasification enter this secondary gasification stage. From this material, the tar-like material and part of the residual carbon 30 (as well as possibly organic sulfur compounds) pass through 8,81140 to stage II according to the gas stream 3. The rest of the fractional carbon is obtained according to the feed stream 4 of the calcium cycle (cf. later text). Air or oxygen (stream 8) is added in a limited way to stage II (partial combustion). In addition to the second-5 gasification reactions, the important reactions of stage II are reactions (4) and (3), in which most of the hydrogen sulfide from stage I reacts according to reaction (4) (e.g. due to suitable temperature and suitable Ca / S ratio) and at the same time causticization-10 reactions (1) and (2) that the CaO required for the sulfur retention reaction (4) is regenerated from CaCO 3 from the calcination reaction 11a (3).

The dissolution of the sodium salts mainly from step I and the causticization step are combined under pressure (1 to 3 MPa) at a temperature of 150 to 250 ° C, respectively.

Due to the higher temperature compared to the traditional method, the reactions (1). (2) and (5) occur relatively rapidly. Separation of calcium compounds is also carried out at elevated pressure (1-3 MPa), so the temperature of the resulting cooking liquor (stream 3: as active chemicals NaOH and NaaS 'is close to the cooking temperature before it is recycled to the cellulose cooking stage.) Compared to the conventional process, this means After causticization, calcium compounds, such as CaCOa from causticization and unreacted Ca (OH) a and CaS (stream 4), are returned to stage II (Ca (OH) a decomposes immediately to CaO). leaving stage I among the sodium salts 30 (stream 9), this carbonaceous material continues to stage II with the calcium circulating stream 4.

9 81140

Any inert material that may accumulate in the calcium cycle and is insoluble can be partially removed from the cycle, if necessary, because the inert particles settle in the aqueous phase at different rates than the calcium compound particles.

5 In this case, the inert compounds in question and the calcium compounds are distinguished from each other.

After the gas treatment according to the invention, other harmful substances (alkali-metal compounds. Solids, etc.) are removed from the combustion gas (stream 5) at a pressure of 1-3 MPa 10 and a temperature of 2,600 ° C, after which the gas is used as fuel in a combined gas and steam turbine power plant. The gas treatment according to the invention (step II) can also be combined, if necessary, with one of the above-mentioned further gas purification steps. For example, it is possible to carry out the time metal removal in step II by using, in addition to the calcium compounds, a suitable chemical which retains the time metal compounds.

Example 2

The implementation alternative according to Example 2 differs from the alternative mentioned in Example 20 in that in this case not all the CaCOara generated in the plant is fed to the gas treatment stage. The amount of material to be fed is only slightly larger than the stoichiometric amount required for reaction (4). The other CaCO 3 and any other compounds that may migrate with it are fed to a separate calcination reactor, for example to another reactor in the gas cleaning line or to a conventional lime kiln. (This fuel can, of course, be used as fuel for the honeycomb). The calcium compound streams 10,81140 (CaO and CaS as main components) from these two 30 different calcination reactors can be fed to the same causticization 1 in or to two different causticization in. The latter option makes it possible to separate the reactions leading to NaOH (reactions (1) and (2)) and the reaction leading to Na = »S (reaction (5)) on the other hand and to do so under the most optimized conditions. .

Example 3

The embodiment of Example 3 differs from the alternative of Cat 1 of Example 10 in that the dissolution and causticization are performed in separate steps. After dissolution, an insoluble material such as residual carbon and an inert material are separated from the solution. The separated material is either returned to the primary gasification step of the waste liquor or thermochemically treated in a separate reactor. This solution is passed to a causticization step.

Example A

In this embodiment, only a part of the total amount of waste liquor in the plant is used for the production of fuel gas, whereby the rest of the waste liquor is incinerated in a conventional recovery boiler process. The raw fuel gas is treated in accordance with the invention, after which the gas is used as fuel for the mill's lime kiln.

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Claims (27)

11 81140 PATENT? REQUIREMENTS 1. A process for treating gas produced from the effluent of alkaline cellulose processes, in particular the sulphate process, characterized in that the gas is contacted with calcium compounds, mainly calcium oxide (CaO), calcium carbonate (CaCO 3) and calcium sulphide (Ca and at a pressure of 0.1 to 10 MPa, with partial or complete retention of gaseous sulfur compounds, mainly hydrogen sulfide (H * S), mainly by reaction (4), and simultaneous partial or complete calcination of CaCO 3 formed during the regeneration of cooking chemicals. notation (reaction (3)); and that the calcium compounds reacted or unreacted in said gas treatment step are then transferred to a causticization step in which CaO and CaS react with sodium carbonate (Na * CO 3) present in the aqueous solution phase according to reactions (1), (2) and (5), after which the insoluble calcium compounds, mainly CaCO 3 and unreacted Ca (OH) * and CaS, are separated from the solution and recycled back to said gas treatment step and the remaining solution containing e.g. sodium hydroxide (NaOH) and sodium sulphide (Na * S) as active cooking chemicals, used in the manufacture of cellulose: reaction 1: CaO + H * 0 Ca (OH) * reaction 2: Ca (OH) * + Na * CO 3 - > CaCO 3 + 2NaOH reaction 3: CaCO 3 - * CaO + CO * reaction 4: CaO + H * S - · CaS + H * 0 reaction 5: CaS + Na * CO 3 - CaCO 3 + Na * S i2 81140 Process according to Claim 1, characterized in that the NaaCOa used in the causticization step comes mainly from the process step (so-called gasification step) in which the gas to be treated is produced from the waste liquor, whereby other solubilizers from the gasification step are also introduced into the aqueous phase. or insoluble compounds. Process according to Claims 1 and 2, characterized in that after the leaching step of NasCOo. 1, the insoluble matter, in particular residual carbon and inert matter, is separated from the liquor cycle and either returned to the effluent gasification stage or thermochemically treated in a separate reactor. Process according to Claim 1 or 2, characterized in that the step of dissolving the Na 2 CO 3 is combined with a step of causticization, whereby in the application according to Claim 2 the possible insoluble matter enters the calcium cycle. Process according to Claim 1, characterized in that only a part of the total amount of CaCOa produced in the plant is calcined in the gas treatment step and the calcium compound stream leaving this step is fed to a different causticization plant than the calcium compound stream from another 25 separate calcination reactors. Process according to Claim 1, 2, 3, 4 or 5, characterized in that the dissolution of Na 2 CO 3, the possible post-dissolution separation, the causticization steps, the post-dissolution separations and the recirculations of the different phases formed in the separation steps are carried out at 0.1 to At a pressure of 10 MPa, however, so that said different steps do not necessarily require the same pressure. A method according to claim 1, characterized in that external oxygen or air is used to achieve the required gas treatment temperature. A method according to claim 1, characterized in that the gas treatment is combined with a secondary gasification step of the waste liquor, in which the material partially unreacted in the primary gasification is further converted. A method according to claim 1, characterized in that the gas treatment is combined with another gas purification step. A method according to claim 1, characterized in that the gas treatment and the gasification of the waste liquor are carried out in the same process. A method according to claim 1, characterized in that said calcium compounds, the small amount of sodium compound carried by the feed streams 20 and optionally other substances form a fluidized bed operating on either the bubble bed or circulating bed principle. Process according to Claims 1 and 8, characterized in that the primary gasification reactor operates on the principle of a fluidized bed (bubbling or circulating bed) and the material taken from the calcium cycle is added thereto. 1 “81140 A method according to claim 1, characterized in that the calcium compound stream from the causticization step is dried before being fed to the gas treatment step. A method according to claim 1 or 4. 5 characterized in that an insoluble matter, in particular an inert substance, different in composition from the insoluble calcium compounds is separated from the calcium cycle, based on the different settling rates present in the aqueous phase of the compound particles in question. A method according to claim 1, characterized in that before or after the gas treatment, those other minor substances which are harmful when using gas as fuel in the combined gas and steam turbine process 15, i.e. the so-called combined cycle power plant. A method according to claim 1, characterized in that all or only a part of the waste liquor is used for the production of the gas, in which case the gas is used as a fuel for the lime kiln, if necessary. No. 81140 A patent for the refining of gas from an alkaline cellulose processor in the form of a sulfate process, the conversion of gas to an ore and contact with calcium formate, a small amount of calcium oxide (CaO), calcium carbonate, calcium carbonate at a temperature of 600 to 1300 ° and a maximum of 0,1 to 0,10 MPa, the color is different from the total retention of the gas at the same level as the solid (HbS), and is of interest in the genomic reaction (4 ) and samtidig, parti ell eller total kalclnering (reaktion 3) av CaCO03 som btldats i samband med regenereringen av kokkemika! iher; och av att de calcium calcium digester som reactor or inte reactor i namnda gasbehandlingssteg overtors dareftereg ka caustiserstst i sodium carbonate (^ 0 ^ 003) som arvarandand 1 vatteniösmngsfasen enligt reactionerna ·. ' I), (2} and (5), varefter olösliga kalciumföremngar, närrnast CaCCh, och CafGH'boch CaS som inte reagerat, separating from the solution and circulating gas to the NaOH and to the other side of the solution as described in Dl a. ) and sodium sulfide (I ^ S) to give: V. cellulosaframställnmgeri: reaction 1: CaO + H-> Q -> Ca (OH) · - reaction 2: Ca (0H) -2+ -> CaCO3 + 2NaOH reaction 3 - CaCÖT -> CaO + CGo. · * L ·. Reaction 4. CaO + H2S -> CaS + H2O reaction 5: Las + Na ^ LO · ^ -> Lacu ^ + NöpS 2. A patent according to claim 1 is used for the purpose of causticizing Na 2 CO 3 to give an interest-free process (hereinafter referred to as a process) for gasification of a producer. varvid till vattenfasen i samband med dess upplosning eventuelH transporteras även andra fran gasfasen härstarnmande antmgen lösliga eller olosiiga föreningar. Z Förfarande enligt. Patent No. 1 or 2. In turn, the solution is separated from the material in the form of a solvent. 4. Förfarande enligt patentkravet 1 eller 2, kännetecknat av ett lösningssteget för ^ CQ? combinator with caustic seals, color detectors in the envelope of 2 möjliga olosta materialet hamnar i K.alciumcirku! ati Onen. 5 Förfarande enligt Pater, tkravet 1. kännetecknat a ··· 'att about en del av den total a mangden av CaCCb som btldas i febnken calcineras igbehand 11 ngss Tege tocnde t1 rande 11 astegav gäe nder ai ci umf ören «ngsf löet en annan kaustisenngsaniäggning än det ka 1 ci um f ören i ngsf 1 öde som kommer f ran den andra separata kalcinenngsreaktom. 6. A patent according to claims 1, 2, 3 or 5 is disclosed in the formulation of Na2CQ ^ e * - * entueH separerinq efter lösningen ... causticizing, separating after causticization and circulating in the separation of the image, the position of the genomic circles ranged from 0.1 to 10 MPa, emellerted at the nervous stagger, in which the overvoltage was measured at the same time. 7. An application for patent protection is provided for in the first instance of the present invention. o. For a patent with claim 1, the terms of reference relating to the application of the patent are set out in the first sentence of this Regulation. 9. Forward patent claims 1. kännetecknat av att gasbehandlingen förbinds med ett ett annat gasreningssteg. 10. Patent application 1. kännetecknat av att gasbehandligen och förgasmngen av avlut sker i en och sarr.ma anordningshelhet. 11. Fcrfarande enligt patentkravet 1 .kännetecknat av att ka! ci urnf öreni ngarna. den ring a mängd natriumforeningar som transp: teräs med matningsströmmarna och eventuella andra ämnen i7 81140 bildaren snarebädd, sorn fungerar enligt bubbelbäda- Eiler cirkulat) onsbäddpri ncipen. ί2. Forfarande enligt patentkraven 1 Eiler δ. kännetecknat a1 · / alt pnmärgasreaktorn fungerar enligt virvelbäddsprincipen (bubbiande Eiler cirkulationsbädd) och däri tiliförs materia! from calcium circulation. 13. For the purposes of claim 1, a reference to the caustic composition of the calcium fortification process is provided. 14. Forward 1 of claim 1, the reverse part of the calcium circulation is separated from the material by means of a molten setting of the calcium-derived sars, which is inert material, on the basis of which the particulate matter is phased out. 15. A claim according to claim 1, which relates to a gas-fired gas engine, and which also involves the use of a gas-fired gasoline and gas turbine processor. i s.k. kombikraftverk. 16. For the purposes of the first patent claim, the scope of this invention includes that of a gas-generating plant, the color of which may be obtained from a branded plant; mesaugn.