FI105717B - Method and arrangement for heat recuperation from a gas flow - Google Patents

Description

105717

METHOD AND ARRANGEMENT FOR THE RECOVERY OF HEAT FROM A GAS FLOW BREAK - FÖRFARANDE OCH ARRANGEMANG FÖR VÄRMEÄ HEALTH-5 AND UR EN GASSTRÖM

The invention relates to a method for recovering heat from a gas stream according to the preamble of claim 1 and to an arrangement for applying the method.

10

The heat energy of a gas stream that contains a significant amount of thermal energy, such as the exhaust gas flow of an internal combustion engine, is most commonly recovered to produce hot water or steam. The steam produced can then be used as process steam or, if desired, further superheated and fed to the steam turbine to generate electricity. Electricity production can be made more efficient by providing heat recovery in several stages under different pressures. Such systems are often complex and expensive.

«« I

<

A single-pressure conventional steam production system

• »I

• «...

I ,; The principles of Fig. 20 are shown in Fig. 1a and Fig. 1b illustrates the

• I

the temperature T of the gas, steam and / or water according to the system as a function of the amount of energy I «. ·.]]. According to Fig. 1a, the gas flow 1 is conducted to the gas • · · ..... ............ ...

• · _ - - through space 2 to recover heat energy from it in three different stages 1 ------------ with heat exchangers. The water supply 3 is directed downstream to the pre-heater 4 at the end of the boiler 2, from where the heated water is supplied to the steam separator chamber 5 and further pumped to the evaporator 6, from which ____ "_______" ... is returned to the steam furnace chamber 5. ----....

passing from the steam separation chamber 5 to the superheater 7, whereby · · • _____; superheated steam is obtained from the outlet pipe 8.

30th ....

1 · 105717 2

1a, it is generally true that, by default, a certain vapor pressure corresponding to a certain temperature and a certain inlet water temperature, it is possible to cool the gas flow only to a certain temperature A after the evaporator 6 and the final temperature B after the preheater 4. Thus, the amount of energy to be recovered is primarily dependent on the vapor pressure and the temperature of the incoming water. The temperature difference between point A and the evaporation temperature, denoted by PP in Figure 1b, is called the so-called. pinch points. The evaporator surface area can be increased to reduce pinch point and enhance heat recovery.

10

Figure 1b shows a gas flow graph 1 'and corresponding graphs of water and / or steam temperatures 4', 6 'and 7' flowing through the preheater 4, evaporator 6 and superheater 7, respectively. Figure 1b shows that a relatively small amount of the gas energy entering the boiler is required to provide a vapor suppression, if the superheat is desired. In the initial portion of the vaporizer 6, energy is transferred from the high-temperature gas 1 'to the vapor generating temperature 6' of the vapor, so that the exergy loss, or loss due to energy conversion, is high during the initial phase of the evaporator 6. This is shown in Figure 1b as the mutual distance between the graphs 1 'and "·. 6'. One solution to reduce exergy losses-

Mi • Y; To this end, various pressure systems based on different pressures have been mentioned, • where steam of different pressures is used.

• ·

I I I

In addition, US 4803958 discloses a known arrangement whereby the heat of the engine exhaust gas and the utilization of an absorption heat pump increase the value of the heat of the engine cooling water to produce useful pressurized steam. Heat is also recovered from the exhaust • · **. ' • · • · «: *] f: only occurs in one step.

Also known from US 4896830 is a solution where the main stream is the recyclable cooling water flow of the engine which is heated in the first stage of the heat exchanger by the engine exhaust gases and from which in a second step, heat is recovered in the heat exchanger by a separate hot water circuit. Here, the exhaust circuit and the hot water production circuit are completely independent. Here again, the heat is recovered from the exhaust gases in only one step. The solution is not related to steam production at all and does not utilize a separate heat pump. A similar solution is also known from US 4911110.

It is an object of the invention to provide a new method for recovering heat from a gas stream, especially from an exhaust gas stream of an internal combustion engine, which makes it possible to minimize the exergy loss by converting the heat energy of a given gas stream to a particular type of steam and thus improving the efficiency of steam production. It is also intended that the application of the method as such is possible with the simplest possible arrangements.

The object of the invention is achieved as set forth in claim 1 and other claims. According to the invention, the thermal energy is recovered from the gas stream both before it is introduced into the evaporator and after the evaporator t <20. After the evaporator, the temperature of the recovered heat energy is increased by mm ·, • ·. ___________.

. ··. utilizing absorption heat pump means such that heat energy recovered prior to the evaporator is supplied to them. Finally, the recovered heat * »: Vi energy is transferred from the absorption heat pump means to the steam generator means to enhance the J. steam generation.

: 25 I ·· --- ----

Thus, according to the invention, a portion is utilized in the gas stream before the · · · -----— i ———

* J

··· 'of the high-value thermal energy of the evaporator to use an absorpmm ·:. ·: A thiol heat pump to cool the gas flow to the evaporator ice, · · ·: .. r * and transfer the recovered thermal energy to a higher temperature,: /. {30 whereby it can be transferred "together with the heat energy acting as the operating energy of the absorbent heat pump through a heat exchanger learning to the vapor generating device. cools more than the evaporator 6 in the normal case shown in Figures 1a and 1b.

5

The solution according to the invention is illustrated in Fig. 2a, which shows, in principle, an arrangement for applying the solution according to the invention. Fig. 2b shows, similarly to Fig. Ib, the temperature T of the gas, vapor and / or water according to the system of Fig. 2a as a function of the amount of energy E.

10

2a, the exhaust gas flow 10 exemplarily from the diesel engine 9 is led to an exhaust boiler 11 having a vaporizer 12 and heat exchangers 13 and 14. These parts correspond to the evaporator 6 only in the case of Fig. 1a. 1a, such as preheater 4 and / or superheater 7, but for the sake of simplicity they are not shown in Fig. 2a. In this case, the preheater 4 would be located after or in parallel with the heat exchanger 14 and the superheater 7 in the exhaust gas flow before the heat exchanger 13.

I I I

.v, 20 The vaporizer 12 cooperates with the steam separation chamber 15, which is

* <I

«(. ·". Equipped with a feedwater inlet pipe 15a and an outlet for the steam produced

«· I

with tube 15b. In addition, the arrangement includes an absorption heat pump 16, which is «·: Y: separately connected to heat exchangers 13 and 14, and heat exchanger means 17 * ·: to transfer heat energy from the absorption heat pump 16 to the steam is not described in further detail here.

In the arrangement of Fig. 2a, the heat exchanger 13 extracts from the gas flow 10 the thermal energy required for the operation of the absorption heat pump 16, which is utilized by the absorption heat pump 16 to cool the gas flow after the steam generator 12 via the heat exchanger 14. The heat energy obtained from the gas stream by means of heat exchangers 13 and 5 105717 14 is then transferred by means of heat exchanger means 17 to a vapor recovery chamber 15. The temperature set by the heat exchanger means 17 is thus that which cools the absorption heat pump 16.

5

In Fig. 2b, the gas flow is marked 10 'and its corresponding graphs of water and / or steam temperature levels in the evaporator 12 and heat exchangers 13 and 14 are marked 12', 13 'and 14'. In Figure 2b, the graphs 14 ', 12' and 13 'together correspond to the graph 6' of Figure Ib. As can be seen in Figure 2b, the difference in distance between graphs 14 ', 12' and 13 'illustrating exer-10 ghase from graph 10' is smaller compared to Fig. 1a, and further, the pinch point PP 'or temperature difference in initial 10 Thus, the temperature of the gas flow 10 has been reduced by the arrangement of the invention in the exhaust gas boiler 2 more than in the known case referred to in Fig. 15b. Accordingly, the amount of thermal energy recovered by the invention is correspondingly greater.

The invention is not limited to the illustrated embodiment, but several variations are possible within the scope of the appended claims. The invention can be applied to «I«. ·. * 20 charges for the various exhaust gas streams of combustion engines and, in principle, which; . for the recovery of thermal energy from any flue gas stream. The invention is applicable »* .......

especially when the vaporization temperature is determined in a certain way p ·: Y: and there are sources of heat «* - v: below the vaporization temperature. In Fig. 2b, by way of example, another heat source, independent of the exhaust gas flow 10, is drawn with dotted lines, from which low-value heat energy can be recovered by an oak exchanger 14 ', which may be desired.

·; · * You can connect the heat exchanger 14 to the medium circuit.

• ......

• * • · · .... ________ • · «· 9 * {.

The absorption heat pump 16 is dimensioned by the temperature 9 · ......... of the heat exchangers 13 and 14.

According to the fluid flows associated with the levels, and as required, several functionally parallel absorption heat pumps may be used.

Claims (5)

1 I! '! Said third heat exchanger (14) recovered heat energy is arranged to in I, ···. transferred (17) from the absorption pumping means (16) to the meadow generating means * <«; (15) to streamline meadow generation. • ·· • 9 • «· •« · • · A method for recovering heat from a gas stream in a system wherein the gas stream is at least passed through such a heat exchanger (12), which acts as an exchanger and to which are connected steam generators (15), whereby · The method utilizes absorption pumping means (16) to efficiently heat-exchange: characterized by the fact that heat energy is recovered from the gas stream bed before its conduction to the exchanger (12) and after the exchanger (12), that the temperature of the heat energy recovered after the exchanger (12) ) is raised by said absorption pump means (16) so that, for these precursors (12), the heat energy obtained for the exchanger (12) is recovered to be transmitted further from the absorption pump means (16) to the meadow generating means (15) to effect the steam generation. Process according to Claim 1, characterized in that, as a gas stream, exhaust gases are used from an internal combustion engine, for example a large diesel engine. 3. An arrangement for applying a method according to any of the preceding claims, wherein an exhaust gas stream (10) is supplied from an internal combustion engine or the like to one or more exhaust gas boilers (11) having at least one such heat exchanger (12), which functions as extender and connected to meadow generating means (15), the arrangement further comprising absorption pump means (16) to effect heat recovery, characterized in that it also belongs to a second heat exchanger (13) for recovering heat energy from the exhaust gas stream ( 10) before its conduit to the exchanger (12) and a third heat exchanger (14) for recovering heat energy from the exhaust gas stream (10) after the exchanger (12), that in said third heat exchanger (14) is the temperature of the recovered heat energy arranged to be raised by utilizing said absorption pumping means (16) so that these are measured in said second heat exchanger (13) recovered heat energy, and that in said second heat exchanger (13) and i 4. Arrangement according to claim 3, characterized in that said extender 25 (12), second heat exchanger (13) and third heat exchanger (14) are arranged in the same exhaust boiler (12). Arrangement according to claim 4 or 5, characterized in that one or more heat exchangers (14 ') adapted to recover heat are connected to said third heat exchanger (14) connecting medium medium circuit (14'). out of medium streams independent of said exhaust gas stream (10).