JP3322280B2 - Method of heat recovery and utilization using chemical energy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering industrial waste heat and the like discharged from power plants, steelworks and various kinds of process equipment using chemical energy and utilizing the heat.

[0002]

2. Description of the Related Art Conventionally, as a method of recovering, transporting and using thermal energy, a method using steam or hot water is generally used. However, these methods are greatly restricted in terms of heat loss and equipment cost, and there is a limit in recovering low-temperature exhaust heat. In other words, energy saving has been progressing in recent years in various energy-intensive industrial facilities such as power plants and steelworks, and a considerable part of waste heat recovery has been performed. Because of the lack of means for proper use, they are often discarded, which requires a large cooling load.

[0003] In recent years, as a method of effectively recovering low-temperature exhaust heat, reducing heat loss, and transporting over a long distance of 10 km or more and utilizing it for district heating and cooling, hot water supply, etc. in urban areas, heat energy is converted into chemical energy to recover heat. And heat utilization is being considered. This method requires the conversion of heat energy and chemical energy on the heat recovery side and heat utilization side, but it can be transported and stored over long distances, has no heat loss during transport and storage, and has a high energy density. Therefore, this method is advantageous in terms of equipment cost.

[0004] The most promising thermal and chemical energy conversion systems are the methanol decomposition reaction of formula (1) and (1) '
A method using a methanol synthesis reaction of the formula has been proposed. CH ₃ OH = CO + 2H ₂ (1) CO + 2H ₂ = CH ₃ OH (1) ′ Since this method is an endothermic reaction of the methanol decomposition reaction of the formula (1), the heat is discharged using the formula (1). The collected C
O + 2H ₂ is transported, and thermal energy is supplied by the exothermic reaction of the formula (1) ′ at the heat utilization site. The methanol produced by the formula (1) 'is circulated to the heat recovery area and reused.

[0005]

The conversion system using the formulas (1) and (1) ′ can be easily reacted using methanol which is inexpensive and easy to handle. Although it seems to be influential, it has the following issues. 1) .Heat recovery is limited by the lower limit temperature of the reaction in equation (1), but from a practical point of view such as reaction rate, the lower limit temperature of heat recovery is around 200 ° C. It is not possible to recover heat in a low temperature range of 200-100 ° C, which is considered to be the most desirable range, to room temperature. 2). In order to carry out heat recovery effectively, it is necessary to lower the lower limit temperature of the equation (1). However, the equilibrium relation of the equation (1) becomes significantly disadvantageous to the methanol decomposition side as the reaction temperature decreases. 3) From the viewpoint of heat utilization, it is advantageous to carry out the reaction of the formula (1) 'at a high temperature, but the equilibrium relationship of the reaction of the formula (1)' is such that the methanol synthesis reaction is significantly disadvantageous as the reaction temperature rises. Become. In order to improve the equilibrium relationship, the methanol synthesis reaction is performed under high pressure. However, heat utilization is low from the viewpoint of equipment cost and operation cost, and it is desired to improve the reaction temperature and pressure characteristics.

[0006] Methanol, which is a medium substance, has great versatility and generality because it is inexpensive as much as fuel price. Therefore, thermal energy and chemical energy conversion using the decomposition and synthesis reactions of methanol will be very effective if the heat recovery temperature is reduced and the heat utilization is improved. It is an object of the present invention to provide a novel method of improving the heat energy and chemical energy conversion system using a decomposition and synthesis reaction of methanol by lowering the lower limit of the heat recovery temperature and improving heat utilization.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on a thermal energy and chemical energy conversion system having the above-mentioned problems, and as a result, by combining the reaction from methanol to methyl formate, it is possible to achieve the recovery of exhaust heat. The present inventors have found that the use thereof can be performed very advantageously, and arrived at the present invention.

That is, according to the present invention, heat recovery is performed by combining the following equations (1) to (3), and the reverse (1) ′ to
This is a method of heat recovery and heat utilization using chemical energy, characterized by performing heat utilization by combining formula (3) ′. _{CH 3 OH = CO + 2H 2} (1) 2CH 3 OH = HCOOCH 3 + 2H 2 (2) HCOOCH 3 = CH 3 OH + CO (3) CO + 2H 2 = CH 3 OH (1) 'HCOO C H 3 _{+ 2H 2 = 2CH 3 OH (} 2) 'CO + CH 3 OH = HCOOCH 3 (3)'

In the present invention, when the equations (2) and (3) are added,
Equation (1) is obtained. Equations (1) to (3) are endothermic reactions and are used for exhaust heat recovery. In heat recovery, the temperature level and the quantity of the heat energy to be recovered correspond to the distribution (2), (1),
It is performed by the endothermic reaction of the decomposition reaction of all or part of the formula (3). Therefore, in the heat recovery, the supplied methanol or methyl formate is transported to the heat utilization side in the form of chemical energy into CO and H ₂ gas.

[0010] The thus recovered thermal energy is transported in the form of a mixed gas of CO and H ₂ , or CO gas or H ₂ gas, and is used for heat utilization. The heat utilization is performed by the heat generated by the decomposition reaction of all or a part of the equations (2) ′, (1) ′, and (3) ′ according to the distribution of the temperature level and the quantity of the heat energy to be supplied. The received CO and H ₂ gas finally becomes methanol or methyl formate which can be handled in a liquid phase, and a part of the chemical energy of the CO and H ₂ gas is released as reaction heat and utilized. Methanol and methyl formate synthesized on the heat utilization side are recycled to the heat recovery side and used as heat recovery medium. Since both media are liquids, they can be stored on the heat recovery side or heat utilization side.

The most important point in recovering exhaust heat of various temperature levels and amounts discharged from various industrial equipments and the like is how to extend the recovery temperature range to a low temperature.
In a one-stage decomposition configuration using only equation (1), it is determined by the reaction characteristics of equation (1). The reaction characteristics can be compared by the equilibrium temperature of the ideal gas and standard state where the free energy becomes zero in the atmospheric pressure reaction.
Since the temperature is 137 ° C., it is difficult to lower the reaction temperature in equation (1) due to equilibrium. The lower limit temperature of heat recovery can be reduced by adding equation (3). The equilibrium temperature of the ideal gas / standard state in Eq. (3) is 6.7 ° C, which is 130 ° C lower than Eq. (1), and therefore (3)
The reaction of the formula has a possibility that the reaction temperature can be remarkably lowered as compared with the formula (1), which is advantageous for heat recovery.

For the thermal energy to be recovered at a high temperature level, the decomposition reaction according to the formula (2) is suitable and advantageous. For recoverable thermal energy at intermediate temperature levels
A decomposition reaction according to the formula (1) can be used. Therefore
The recovery target thermal energy whose temperature level has been reduced by performing the heat recovery according to the equations (2) and (1) can be further recovered to a lower temperature by the equation (3).

The combination of the thermal energy to be recovered and the formulas (1) to (3) is not fixed, but is in the most suitable form in consideration of the above considerations, that is, the individual temperature level and amount of the heat source to be recovered. The optimum configuration is used according to the reaction characteristics of the equations (1) to (3). Reaction choices include, for example, (1), (2),
Various combinations can be performed, such as when using all of equation (3), when using equations (1) and (3), when lacking equation (2), when using only equation (3), and so on. This combination is mainly adapted to the calorific value distribution according to the temperature level of the thermal energy to be recovered, and the burden ratio of the conversion reaction formulas (1), (2), and (3), which is the most advantageous as a whole system, is reduced. The configuration is determined.

The transport of the recovered heat is a mixed gas of CO and H ₂ converted into chemical energy, or CO gas, H
It takes place in the form of _two gases. Although gas is difficult to transport, it is not necessary to consider heat loss because it is converted into chemical energy.

As described above, heat utilization is performed by using (1) ', (2)' and (3) '
It is carried out by the exotherm of the synthesis reaction using the formula It is advantageous in terms of heat supply to perform these synthesis reactions at as high a temperature as possible. The reaction temperature can be easily increased to a certain extent by changing the pressure conditions by pressurization, but pressurization naturally involves an increase in cost and consumption of motive energy. Therefore, it is advantageous in terms of operating power to perform the reaction pressure at a pressure as low as possible in consideration of the pressure loss of the entire system, and as a whole, an increase in the synthesis reaction temperature and a decrease in the pressure are in conflict with each other. Will determine the optimal harmony point according to the operating conditions of the whole system.

The medium substances synthesized by the formulas (1) ', (2)' and (3) 'are methanol and methyl formate. Methanol is synthesized in a single step of the formula (1)'. There is a method of combining in two steps by the formulas 2) 'and (3)', and the optimum ratio of the burden on both methods is determined by the operating conditions. The formation of methyl formate is the residue consumed in methanol synthesis in CO and H ₂ transported to the heat utilization side. From the equilibrium relationship,
If the temperature level of the exothermic component for heat utilization is 140-150 ° C or higher, the methanol synthesis will proceed with the two-step synthesis reaction according to the equations (2) 'and (3)' according to the one-step synthesis according to the equation (1) '. Practical use is advantageous in practical use.

The methanol and methyl formate synthesized on the heat utilization side are transported to the heat recovery side and reused for heat recovery. Both medium substances have a boiling point of 64.5 ° C. and 31.8 ° C., respectively, so that they are liquids under standard conditions, so that a closed piping system, a transport system such as a ship or a lorry, and a storage tank can be used.

In contrast to the conventional one-step methanol method in which the decomposition reaction and the synthesis reaction are only one kind of reaction according to the formulas (1) and (1) ', respectively, the method according to the present invention uses methyl formate as a medium substance. By adding, the decomposition reaction becomes (1),
(2), (3), (1) + (2), (1) + (3), (2) + (3), (1) + (2) +
Since the combination of the seven types of reactions in (3) can be selected, and the combination of the seven types of reactions can also be selected for the synthesis reaction, heat recovery and heat demand composed of various temperature levels and amounts of heat energy can be selected. A configuration that can perform a reaction most suitable for the above can be obtained.

However, on the other hand, in the method of the present invention, decomposition /
The combination of the heat recovery reaction and the synthesis / heat utilization reaction needs to be configured to accommodate various operating conditions. In particular, it is advantageous to concentrate the selection of a decomposition reaction in a single heat recovery target equipment on a specific reaction. On the other hand, if the heat recovery target equipment is huge like a steel mill, or if there are many heat recovery target facilities and collectively perform large-scale heat recovery,
All the decomposition reactions of equations (1), (2) and (3) will be used.

In any of the decomposition / heat recovery reactions of the method of the present invention, the supplied heat transfer medium is methanol and methyl formate, and the heat transfer medium produced is a mixed gas of CO and H ₂ ,
Or CO gas and H ₂ gas. As described above, the reaction amount ratio of each reaction is determined so as to obtain an optimum configuration in consideration of the characteristics of each decomposition reaction. According to the reaction ratio, the total amounts of the generated heat medium substances, CO and H ₂ , are determined.

As for the selection of the synthesis / heat utilization reaction, it is advantageous to combine a reaction at a high temperature, which is advantageous for heat utilization, with a reaction having reaction characteristics with a small power load for pressurization. However, the ratio of the amounts of methanol and methyl formate, which are the heat transfer medium produced in the synthesis / heat utilization reaction, is uniquely determined by the ratio of the received H ₂ / CO. Therefore, the choice of the synthesis / heat utilization reaction is to select whether the methanolization is performed in a one-step reaction of formula (1) 'or in a two-step reaction of (2)' + (3) '. When the level is 140 to 150 ° C. or higher, a two-stage reaction system is advantageous in terms of equilibrium.

The six kinds of reactions used in the present invention are composed of three kinds of equilibrium reactions which are reversible to each other, and the selectivity is 10%.
In the case of 0%, there is no problem on the balance, but since it is a chemical reaction, there are some side reactions and accumulation of CH ₄ , CO _{2 and the} like may occur. Since these by-products are mainly concentrated in the outlet gas of the synthesis / heat utilization reaction, they are recovered by separating and burning. At this time, the substance to be replenished is methanol. Methanol is an inexpensive substance close to the fuel price, and therefore, the economic loss associated with the processing of by-products can be suppressed to a small level.

[0023]

The following examples show six examples of the reaction utilized in the present invention. The operating conditions of each reaction differ depending on the catalyst used, and the amount of each reaction is determined by the set conditions in the heat recovery reaction and the heat utilization reaction, and may be a gas phase reaction or a liquid phase reaction. Therefore, the present invention is not limited by these examples.

Example 1 [Example of reaction of formula (1)] A reaction tube having an inner diameter of 14 mm was charged with 20 ml of a Cu-Ni-Al-P catalyst.
A methanol decomposition reaction was performed according to the formula. The reaction was carried out at a normal pressure of 280 ° C. under a methanol supply of GHSV 2000 Hr ^−1, and the conversion of methanol was 97.9% (equilibrium conversion: 99.9%) and the CO selectivity was 99.98%.

Example 2 [Reaction Example of Formula (2)] The reaction tube of Example 1 was charged with a Cu-Zn-Al-P-Li catalyst.
A methanol dehydrogenation reaction was performed according to the formula. The reaction was carried out at 260 ° C. at a pressure of 5 kg / cm ² G at a GHSV of 3500 Hr ⁻¹ with methanol supplied, and the conversion of methanol was 36.5% (equilibrium conversion 3
7.6%), and the selectivity for methyl formate was 93.0%.

Example 3 [Example of Reaction of Formula (3)] In a closed circulation type reactor having a capacity of about 360 ml, 35 mg of methyl formate and Na / MgO catalyst were charged and reacted at normal pressure of 100 ° C. CO and methanol were generated from methyl formate, and the conversion of methyl formate after 120 minutes was 60% (equilibrium conversion: 95.7%).

Example 4 [Reaction Example of Formula (1) '] A reaction tube having an inner diameter of 8 mm was charged with 0.5 ml of Cu-Zn-Al-B catalyst.
(1) ′ A methanol synthesis reaction was performed according to the formula. H ₂ 69.0%
, CO 31.0% raw material gas is supplied at SV 20000Hr ^-1
As a result of performing the reaction at a pressure of 70 kg / cm ² G at 260 ° C., the conversion from CO to methanol was 29.5% (equilibrium conversion: 72.0%).

Example 5 [Reaction Example of Formula (2) ′] The reaction tube of Example 4 was filled with a Cu—Cr catalyst, and methyl formate and H ₂ were reacted at 100 atm and 220 ° C. As a result, the conversion of methyl formate was 85% (equilibrium conversion: 86.5%), and the selectivity to methanol was 95%.

Example 6 [Example of reaction of formula (3) '] Metal potassium was added to a 2-liter rotary autoclave.
820 g of a 27 g methanol solution were charged. The autoclave was sealed and the solution temperature was raised to 80C. Then CO was introduced until the pressure reached 100 atm. This pressure drop confirmed that methyl formate was produced at an initial rate of 32.6 g / min. Then CO was introduced until an equilibrium pressure of 100 atm was reached. After the temperature was reduced to 25 ° C. and the pressure was reduced, the composition of the reaction product (1220 g) was analyzed by gas-liquid chromatography, and as a result, the content of methyl formate was 60% by weight.
The methanol conversion was 50% (equilibrium conversion 80.2%).

[0030]

According to the present invention, methyl formate is added as a new medium chemical substance to the conventional thermal energy and chemical energy conversion system using methanol, and has the following effects as compared with the conventional method. 1) On the heat recovery side, it is possible to respond by three reaction formulas, and the heat recovery compatibility is improved. In particular, the decomposition reaction formula (3) of methyl formate is advantageous to the low temperature side in terms of equilibrium as compared with the reaction formula (1) of methanol decomposition, and the heat recovery range to the low temperature range is extended. 2). The number of reactions also increases on the heat utilization side, so that the responsiveness to heat utilization is improved. Especially the hydrogenation reaction formula of methyl formate
(2) ′ is advantageous on a high temperature side in terms of equilibrium as compared with the methanol synthesis reaction formula (1) ′, so that an exothermic reaction at a high temperature becomes easy, and there is a possibility that heat utilization can be advantageously performed. 3) .Methanol and methyl formate synthesized on the heat utilization side are recycled and reused as a heat recovery medium.
Since both medium substances are liquid, they can be easily stored on the heat recovery side and the heat utilization side, and can cope with heat recovery and heat utilization in various ways.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-125564 (JP, A) JP-A-55-149641 (JP, A) JP-A-60-200064 (JP, A) JP-A-56-125 88801 (JP, A) JP-A-1-233241 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F25B 17/02 C09K 5/00 F24J 1/00 F28D 20/00

Claims (1)

(57) [Claims] The present invention is characterized in that heat recovery is performed by combining formulas (1) to (3), and heat is used by combining formulas (1) ′ to (3) ′ in the opposite direction corresponding to each formula. the method of heat recovery and heat utilization using chemical energy to _{CH 3 OH = CO + 2H 2} (1) 2CH 3 OH = HCOOCH 3 + 2H 2 (2) HCOOCH 3 = CH 3 OH + CO (3) CO + 2H 2 _{= CH 3 OH (1) '} HCOO C H 3 + 2H 2 = 2CH 3 OH (2)' CO + CH 3 OH = HCOOCH 3 (3) '