NO800960L - PROCEDURE FOR AA IVARETA HEAT THAT RISES IN A HEAT PUMP - Google Patents

Description

The invention relates to a method for utilizing heat energy, based on the use of a heat pump, whereby a heating medium or one or more medium* streams is connected to a heat pump system's "evaporation device" and where a medium stream, which is to be heated, is connected to the condenser device array.

A device by means of which heat energy is transferred from a lower temperature to a higher one is known as a heat pump.

The idea of using a heat pump for heating and for utilizing waste heat has long been known. Regarding the state of the art relating to the present invention, reference is generally made to the publication: "Possibilities till och effects of using a heat pump vid upp-varamning och vid tillvaratagande av varme", Aittomåki, Kalema, Lappalainen, Talsio, Wikstéri, STFLaboratoriet f<5r WS- technique, notice 23, Otnas, March 1975, concerning special solutions for the publication - "Refrigeration Engineering", H.J. MacINtire, F.W. Hutchinson, John Wiley & Sons:,Inc, New York,- 1950, Chapter VI.

The technical performance capability of a heat pump can be seen from a heat coefficient e, where e = released heat output/performed work, where the released heat output is the sum of the heat output taken from a heat source and the performed work. The benefit of the heat pump is thus essentially dependent on the size of the heat coefficient. The larger the coefficient e is, the more useful the heat pump is. It can also be easily proven that the theoretical heat coefficient for a heat pump system with a circuit can be expressed as follows:

where t= the temperature of the medium stream to be heated after the heat pump, and

T= the temperature of the heat-emitting medium flow after the heat pump,

why the heat coefficient depends on it

prevailing temperature.

Previously known heat pump systems have, in the main, only included a single circuit. In other words, only one medium can be used in this to transfer heat from the heat source to the object to be heated.

The theoretical heating coefficient in such a heating system with a circuit is even with modern adaptations less than four depending on the size of. the temperature of the medium to be heated and/or of the heat-emitting medium. The theoretical heat coefficient for the heat pump systems that are currently in general use can be calculated according to the above-mentioned formula (1). Those losses

which is connected to the compressor and also to other parts of the heat pump system, however, further lowers this theoretical heat coefficient. The most important of these sources of loss is the non-ideal operation of the compressor. Based on the above, it is also essential to keep the compressor's efficiency within the optimum range in order to achieve a good heat coefficient. The operating point of the compressor should thus be selected within the range of the optimum pressure ratio (pressure side pressure/suction side pressure), and overheating of the gaseous medium to be compressed should be prevented to the greatest extent possible. Overheating reduces the efficiency of the heat pump system. However, this is not possible, not even in connection with modern known special solutions, according to which the pressure ratio in this system is determined by the temperature levels that require adjustments and by the properties of the media used. It is also not possible to avoid overheating, which results in reduced efficiency in the system with a single circuit.

The heat coefficient for known heat pump systems with a circuit also varies with modern adaptations, most often between 2...3 for the reasons mentioned above.

As an example of the state of the art regarding heat pump systems with multiple circuits, reference is made to DE Patent No. 2,637,230 and US Patent No. 4,124,177.

Electricity is primarily used as the drive energy for heat pumps. In several countries, i.a. in Finland, due to the production method, electricity is significantly more expensive than heat energy. In Finland, the price ratio electricity/heat energy today usually varies between 2.5 4 depending on the tariff policy.

Under such conditions, it is natural that the heat pump, despite all precautions aimed at saving energy, has not been able to arouse any greater interest. Due to the limited supply of energy throughout the world and to ease the financial burdens arising in a

countries that are not self-sufficient in terms of energy and which. must therefore import energy and fuel, it would therefore be important to develop a heat pump system whose heat coefficient is significantly higher than the prevailing price ratio between electricity and heat energy.

The purpose of the present invention is therefore

to provide a method for the utilization of heat energy based on the use of a heat pump, and which enables the achievement of a heat coefficient which is significantly higher than the coefficients known today and which thereby enables heat utilization also within such applications as

prevails where previously this was not financially possible.

To achieve the above stated, the invention is characterized in that the heat pump system, in order to improve the heat coefficient, comprises several continuously working separate heat pump circuits, whose compressors are provided with a common drive device, and that the heat pump circuit's capacitors are connected in series in relation to the medium flow to be heated, so that the temperature of the medium stream to be heated rises when it is in heat exchange contact with the media circulating in the heat pump circuits' condensers.

Theoretically, the invention is most advantageous when the system according to the invention comprises an infinite number of separate heat pump circuits. By considering the increase in the heat coefficient e as an increase in the number of used circuits according to the invention and that the increase in the circuits, at least in the hitherto known technique, also to some extent

increases the installation cost, one achieves that an optimal result is achieved by using a system with 6.....10 separate heat pump circuits. Hereby, the circumstance that the heat coefficient e first rises relatively steeply, as the number of arranged heat pump circuits according to the invention increases, is used in an efficient manner. However, the increase in the heat coefficient decreases with a larger number of circuits.

The invention will now be described in more detail with reference to some embodiments of the invention which are shown in the drawings, where: figure 1 schematically shows a heat utilization system with six circuits according to the invention,

figure 2 shows the temperature distribution in the different circuits in the system according to figure 1,

figure 3 shows the theoretical total heat coefficient e]co]c' which is obtained with the method according to the invention, as a function of the number of separate heat pump circuits with the temperature according to a later described example.

figure 4 shows a T-s coordinate system the physical reason for such an advantageous embodiment of the invention, where the medium circulated in the heat pump circuit and evaporated in the evaporator is kept suitably moist when it reaches the compressor in the heat pump circuit,

figure 5 shows a connection core for a heat pump system according to the invention used in connection with the utilization of the heat energy in waste water,

figure 6 shows a heat pump system with several circuits according to the invention used in connection with a drying device for wood, i.e. a general view of a condensation dryer: in which the method according to the invention is used,

figure 7 shows a connection core for the heat pump system in the condensation dryer in figure 6,

figure 8 shows a mechanical embodiment of the compressor and expansion valves in a heat pump system with 6 circuits, and

figure 9 shows a section along the line IX-IX on

figure 8.

An embodiment of the method according to the invention will now be described with reference to figures 1 and 2. The heat utilization system according to figure 1 comprises 6 heat pump circuits P^-Pg" whose evaporators H^-Hg are connected to each other in sequence in accordance with rising evaporation temperature T^_^ (k=l-6) in series and in heat exchange contact with a waste water flow M. The heat pump circuits P^-Pg condensers L^-Lg are similarly connected to each other in sequence in accordance with rising condensation temperature t^ in series and in heat exchange contact with water flow m to be heated. Each and every heat pump circuit p^-pg also includes, in and of itself, known compressors K^-Kg and expansion valves T^ - .

Figure 2 shows the temperature levels T, and in the various heat pump circuits p^-Pg in the system according to Figure 1. The temperatures of the medium flow M which emits heat is denoted by Tcog and the temperature of the medium flow to be heated is denoted by t. According to Figure 2, the temperature T decreases in the direction of the heating medium flow M. The temperature t c rises in turn in the direction of flow of the medium flow m.

Hereafter, the improved effect which the inventive method has on the heat coefficient e is explained with reference to figures 1 and 2.

The ratio between the heat capacity flows for the waste water and the water to be heated (heat capacity flow = medium flow x specific heat, [ cl = fel = W/K) is denoted by a(a = C/c). Initially, it is assumed that the compressor's K isotropic efficiency nj_s= 1. Using this, it can be shown that the system's theoretical heat coefficient (e^^) is

there

N is the number of heat pump circuits.

Furthermore, it can be proven that an optimal circuit distribution (gets the maximum value) is present when Tk+]/T]c= Tk/Tk-1, i.e. Tk+i/Tk= constant = m.

This reduces S.T to the form:

N

where m is determined by the formula m= (Tn/Tq) -*-/n. Furthermore, it can be proved that .--

Example t = 323 K T = 3 23 K T = 28 3 K a=l c— o N o

Hereby, the heat coefficient for a heat pump system realized with optimal circuit distribution with N stages: is now m= (323/283) 1/Nf and for a heat pump system equipped with an infinite number of circuits

By giving N a numerical value, the graphical presentation in figure 3 is obtained, where e^q^.<a>symptotically approaches the above calculated value of 8.08 as N increases.

The theoretically best possible heat coefficient in connection with previously known common systems with a circuit is therefore only 4.04 according to the values in the example. In connection with a system with, for example, 30 circuits, the coefficient is already as high as 7.81. In the system shown in Figure 1 with 6 circuits, echo^6.8, i.e. approx. 70% higher than in a system with only one circuit.

With a system with several circuits, on the other hand, in comparison with a system with one circuit, two important and practical additional advantages are also achieved which affect the efficiency of the compressor. To. these advantages have previously been referred to.

Firstly, the compressor keeps K pressure feed (pressure in its pressure/suction side pressure) suitably large as each and every circuit works with a relatively small temperature difference (condensation-evaporation). This enables the compressors to work within the range of their optimum efficiency. In a system with one circuit, the pressure ratio becomes large due to the temperature difference, whereby the efficiency of the compressors (ti.) is significantly lower.

Second, a multi-circuit system enables the use of different media in the various circuits and allows the media in the various circuits to be kept suitably moist as it reaches the compressor. A system with one circuit has in and of itself the natural limitation that only one specific medium can be used. This has constituted a factor that limits the system's application as it is clearly difficult, often even impossible, to find a medium that is suitable for a large temperature range. In a system with several circuits, this does not pose any problem, as the most suitable medium can be selected for each circuit on the basis of the temperature range prevailing in the circuit, independently of the other circuits.

When treating liquids in 6 circuits according to figures 1 and 2 at temperatures according to the example described above, for example for the circuits { P2_' P2'^ >3^ On the cold side of figure 1 a suitable medium can be selected where R21 and for the circuits (p ^p^Pg). on the hot side a suitable medium Ril.

The way in the heat pump circuit P^~PNcirculating medium evaporated in the evaporator is kept suitably moist when it comes to the compressor K will be described in more detail hereafter with reference to figure 4.

Figure 4 shows the circulation process in the heat pump circuit in a T-s coordinate system. It may prove that the point F is the best, the point for the beginning of the compression work. The point F is determined by the point of intersection. between the isotropic passing through the point P and the isotherm T-^. The location of this point is the same for all values of the isotropic efficiencyfl^g*The steam humidity at point F must be x. Hereby it can be proved that

where Ah^= the heat of vaporization at the temperature T^.

C the specific heat of the medium (liquid).

Cp = specific heat of the medium (steam).

Hereafter, it will be shown with the help of an example that the choice of compression site has a significant impact on the heat coefficient.

As an example, a case is examined where the medium is water vapor and T-^= 321.6 and T 9= 369 K. The compressor's n. must be =0.7. In previously known heat pump solutions, the suction side is located at point F^" (fig.4), whose temperature is approximately 10-30°C higher than .

When the compression starts starting from the point F"*" (superheating 30°), one can calculate that e= 4.7, i.e. the coefficient is significantly worse than when the compression started at the point F, whereby e-= 5.5. In reality, this difference is even greater as the overheating also means that the temperature difference between the heat source and the medium must be correspondingly greater. This circumstance has not been taken into account here.

The improvement discussed above lies in

that the volume also has a tendency to increase when the temperature of the gas rises sharply due to the adiabatic compression, and if no cooling is provided, a lot of extra work must be done due to the increase in volume of the gas to reach the desired condensation temperature heat pressure. About the gas

brought to compression in a moist state, the vaporized liquid effectively cools the gas, whereby the necessary "unnecessary" additional work is reduced and the heat coefficient is improved. In practice, the steam content on the suction side can be regulated to a suitable value, among other things...-.by regulating the temperature on the pressure side, e.g. by means of the compressor K revolutions.

Hereafter, the embodiment of the system is described in detail in Figures 1, 2 and 5:

waste water quantity 1.87 kg/s

- the wastewater inlet temperature Tg=313.K and outlet temperature T =283 K

o

- water flow to be heated 1.87 kg/s

- output temperature for the water to be heated tQ=313 K.

According to an optimal temperature distribution, T1=287.8K, T2=292.7K, T3=297.6K, T4=302.6K and T5=307.7K. The following temperatures are selected T1=288K, T2=293K, T3=298K, T4=303K and T5=308K.

It is assumed that the K isotropic efficiency of the compressor is nj_s=0.65 and that the T isotropic efficiency of the expansion turbine is n = 0.3.

. The system's suitable main dimension value is given below in tabular form:.

-total heat output 286 kw

-total compressor power 52kW

-total turbine power 1 kw

-total electrical power 52-1= 51kw

-heat coefficient e = 286/51 =5.6

For comparison, the following heat coefficients are calculated for this example: - theoretical upper limit for the heat coefficient with formula (5) (for a system with an infinite number of circuits): - theoretical upper limit for a system with 6 circuits with formulas (4) and (2): -theoretical upper limit for a system with 1 circuit:

Hereinafter, with reference to figures 5-9, some examples of devices for carrying out the method according to the invention are described. Figures 5, 8 and 9 show an advantageous embodiment of a device for using the system according to the figure. 1 and 2.

An electric motor M arranged on a stem 14. drives by means of a coupling. 11q a first expansion turbine group T^., T , and T ^. A shaft 10 driven by means of a coupling 111 drives a gear 12a, which in turn drives the gears 13^, 132, 13^. The gears 13^, 132, 133 turn the screw compressors K^, K2, K^. The sizes of the gears 13-^, 132, 13^ can be chosen so that they are different in between to provide the desired volume flow.

The plant also comprises another compressor group, K 5 and Kg, which is driven by a large gear 12b connected to the shaft 10 by means of the gears 13^, 13,. and 13g. In Figure 5, the aforementioned gear ratios are schematically denoted by the reference numbers ll^....llg.

The evaporators H^..Hg and the condensers L^.... Lg

in the heat pump circuits p^...pg. is of ordinary construction and

previously known why it is not necessary in this context to describe their construction in further detail.

With reference to figures 6 and 7, such an embodiment of the invention is described below, where the heating medium flow and the medium flow to be heated are one and the same medium flow. Figure 6 shows a schematic section of a condensation dryer for stacks of wood and Figure 7 shows a connection core for a heat pump system with several circuits according to the invention which is used in this dryer. The dryer consists of a drying house 20. Inside the house there are rails arranged in a manner known per se, on which a cart 21 equipped with wheels 22 rolls. The drying wagon 21 is loaded with moist timber P, through which a drying

air flow is led via channels 30 and 31. Channels 30 and 31 are bounded below by inclined walls 24a. and 24b. The distance between the lower edges of the walls corresponds to the width of the working load P. A fan 26 driven by the motor 25 is arranged above the working load P, which in turn provides the air circulation through the working stack P. The outgoing air flow that passes through the working load P..is.denoted with an arrow F,. This air flow divides into two branches F^ and F^n« Regarding the air flow F^n refer to Figure 7, according to which this flow goes in accordance with the invention through the evaporator H^-Hg in the heat pump circuit P^~Pg• The evaporators in Figure 6 are all denoted by the reference number 27. In the evaporators H, the air stream Fi is cooled. n o•g dries, so that its moistureXg > xq. The same air flow F is passed through the condensers I^-Lg in the heat pump circuits P^~Pg whereby the air is heated. The mentioned system includes 6 heat pump circuits p^-pg. The circuits are provided with compressors K^-Kg and expansion turbines T^-Tvg, which are connected in the manner described above and shown in Figure 7 and which are provided with power transmission devices such as those shown in Figures 8 and 9. In Figure 6, the from the evaporator H (27) to the condenser L (28) with the help of the heat pump transferred heat flow denoted by arrows W. Out of the above described system comes a dry and warm air flow Futf. which mixes with the moist cold air stream

F^, so that one mixture with both suitable temperature and suitable humidity (xq) is provided, which in the form of a current f 2 is carried through the stack with work P.

Above, such embodiments of the invention have been described where the temperature of the heating medium flow (M) drops when the flow passes through the evaporator (H^...K^) in the heat pump circuits (p^...p^).

The system with several circuits according to the invention can, however, within the framework of the inventive idea, also be used in such cases where the heating medium flow (M] is not an actual medium flow, while on the other hand, soil, lake water, sea water etc. are used as the heat source.

The invention can also be used in such a way that several different medium streams are used as heating medium which are distributed to the various heat pump circuits (p^)

in accordance with the temperature of the various medium streams, e.g. in such a way that a distribution T0~TN_^ of the temperatures (T^) according to Figure 2 is obtained. If, for example, deep seawater is used as a heating medium, a temperature distribution according to Figure 2 can be provided by taking seawater from different depths, whereby the water's temperature varies.

The various details of the invention may vary within the scope of the invention idea defined in the patent claims below.

Claims (8)

1. Method for utilizing heat energy, based on the use of a heat pump whereby a heating medium or one or more medium streams (M) has been connected to the heat pump system's evaporator devices (H) and a medium stream (m), to be heated, has been connected to its condenser device (L), characterized in that the heat pump system in order to improve the heat coefficient either (e) comprises several continuously working separate heat pump circuits (P^~PN) in whose compressors (K^-K^) are provided with a common drive device and that the heat pump circuit's capacitors (L^ -L^ ) are connected in series in relation! .to the medium flow (m) to be heated, so that the temperature (t) of the medium flow (m) to be heated rises when it is in heat exchange contact with media circulating in the heat pump circuits <s> (P ^<_>PN ) capacitors (L^ -LN ). 2. Method according to claim 1, characterized in that the medium flow (M) is used as an emitter of heat energy, and that the heat-emitting and the heat-receiving medium flow (M,m) are connected in counterflow by means of the heat pump circuits, so that the heat-emitting medium flow (M ) temperature (Tc) decreases as it passes through the heat pump circuit's (P^-PN) evaporators (H^-H^) 3. Method according to claim 2, characterized in that the ratio (Tk/Tk _1 ) between the evaporation temperatures for the medium in all two consecutive heat pump circuits is constant. 4. Method according to claim 1, 2 or 3, characterized in that in the separate heat pump circuits (Pj -PN ) the circulating medium, which after the evaporators (H-^ -t^) is in a gaseous state, is kept suitably moist hair that comes to the compressors (K^-K^) in the heat pump circuit (figure 4). 5. Method according to claims 1, 2, 3 or 4, characterized in that different heat transfer media are used in the different heat pump circuits (p-^-p). 6. Method according to claims 1, 2, 3, 4 or 5, characterized in that the heat-emitting and the heat-receiving medium flow are made up of separate medium flows (M,m), which are connected counter-currently to each other by means of the heat pump circuits (P^~PNJ• 7. Method according to claim 1,2,3,4 or 5, characterized in that both the heating and the heat-receiving medium flow are made up of the same medium flow (F), which is connected to flow countercurrently at the evaporators and condensers in the heat pump circuits (P^~PN )• 8. Method according to claims 1-7, characterized in that the heat pump system comprises at least four, preferably 6-10 separate heat pump circuits (p^).