JP5769257B2 - Cogeneration system heat storage control method - Google Patents

Description

  The present invention relates to a hot water storage control technology for a cogeneration system, and more particularly, to a hot water storage control technology for a cogeneration system that can efficiently store hot water in a small-scale system for home use.

The cogeneration system is a combined heat and power system that recovers waste heat generated during power generation and creates hot water at the same time and stores it in a hot water storage tank to meet the demand for hot water supply. Patent Document 1).
Currently, commercial cogeneration systems using commercially available fuel cells and the like have a large capacity as a backup water heater (for example, 24) in order to prevent running out of hot water when using a large amount of hot water supply when the amount of stored heat is small. It is common to install a water heater of about No.).
Furthermore, in the cogeneration system 100 of Document 2, as shown in FIG. 8, a backup burner 104a that uses city gas or the like as fuel in the fuel cell device 101, and reformed gas generated by the reformer 102 is used as fuel. A backup water heater 105 having a process gas burner 104b is provided.

JP 2006-183947 A JP 2004-164868 A

However, the installation of a large-capacity backup water heater becomes a cost increase factor and an impediment to the spread of cogeneration systems.
An object of the present invention is to provide a hot water storage heat storage control technique that uses a small water heater as a backup water heater for a cogeneration system and can avoid the risk of running out of hot water when using a large amount of hot water.

The gist of the present invention is as follows. That is, the hot water storage control method of the cogeneration system according to the present invention is:
(1) In a cogeneration system comprising a hot water storage tank for storing generated exhaust heat as hot water in a hot water storage tank, and a backup water heater for replenishing the shortage of heat storage amount,
Predicting the balance between the heat storage amount and hot water supply demand in each time zone τi (i = 0 to n) belonging to the predetermined prediction target time zone (t0 to tn), before the start of the time zone where shortage is predicted at the latest The backup water heater is operated so as to complete heat storage for the shortage.

(2) In the invention of (1) above,
(A) For each time zone τi (i = 0 to n) from the current time (t0), based on the prediction of hot water supply demand D (τi) and power generation exhaust heat recovery amount H (τi), A step of obtaining a hot water storage tank heat storage amount Q (ti);
(B) For each time period, determining a supply and demand balance between the hot water supply demand D (τi) and the hot water storage tank heat storage Q (ti);
(C) In the invention of (2) above, in any time zone (τj), when the hot water storage tank heat storage amount Q (tj) is lower than the hot water supply demand amount D (τj) in the time zone, at the latest time Performing a heating operation of the backup water heater so as to maintain Q (tj) ≧ D (τj) before the start of the belt;
(D) repeating the steps (a) to (c) every predetermined update time;
It is characterized by including.

(3) In the above invention (2), instead of the steps (b) and (c),
(E) For each time zone, the hot water storage tank heat storage amount Q (ti) and the hot water supply demand total ΣD (τk) (k = i to i + m) for the subsequent multiple time zones (τi to τ (i + m)) Determining a supply-demand balance;
(F) In any time zone (τj), the hot water storage tank heat storage amount Q (tj) is the total hot water supply demand amount ΣD (τk) (k = j) for the subsequent multiple time zones (tj to t (j + m)). ~ J + m), the step of performing the heating operation of the backup water heater so as to ensure Q (tj) ≧ ΣD (τk) at the latest before the start of the time period,
It is characterized by including.

(4) In the invention of (2), in the step (c), the hot water storage tank heat storage amount Q (t0) at the start of the latest time zone (τ0) is the hot water supply demand amount D (τ0) in the time zone. If it falls below, the heating operation is performed at the maximum output qmax of the backup water heater.
It is characterized by that.

(5) In the invention of (2), in the step (c), when there are a plurality of time zones in which the hot water storage tank heat storage amount Q (ti) is lower than the hot water supply demand amount D (τi), the backup water heater When the heating operation is performed at the maximum output qmax, the operation is started at the operation start time in the time zone where the operation should be started earliest.

(6) In each of the above inventions, the prediction target time zone is a time required to fully store the hot water storage tank only by the backup water heater.

(7) In each of the above inventions, when the hot water storage heat storage amount Q (t) reaches a state below the predetermined minimum heat storage amount Qmin during the control, the backup is performed until Q (t) ≧ Qmin. The heating operation of the water heater is performed with the highest priority.

  According to the present invention, it is not necessary to mount a large-capacity backup water heater, so that the apparatus / equipment can be reduced in size and weight, contributing to resource saving and initial cost reduction.

  In addition, since the necessary amount of hot water is always stored before the time when hot water supply demand is predicted, there is an effect that the risk of running out of hot water can be avoided.

  Further, since the hot water storage is controlled to be completed immediately before the time when the hot water supply demand is predicted, there is an effect that the heat loss from the can can be minimized.

  Further, in the invention in which the backup water heater performs the heating operation at the maximum output when it falls below the predetermined minimum heat storage amount Qmin, even if the demand for hot water supply is deviated, There is an effect that inconvenience can be avoided or suppressed as much as possible.

It is a figure showing the composition of cogeneration system 1 concerning a first embodiment. It is a figure which shows the hot water storage heat storage control flow in 1st embodiment. It is a figure which shows the hot water storage heat storage control flow of long-term prediction. It is a figure which shows the example of (DELTA) Q (ti)> 0 in all the time slots in long-term prediction. It is a figure which shows the example of (DELTA) Q (ti) <0 in any time slot | zone in long-term prediction. It is a figure which shows the example of Q (t1) <D (t1) in short-time prediction. It is the figure which showed heat storage amount transition by heating operation compared with the case of no heating. It is a figure which shows the hot water storage heat storage control flow in 2nd embodiment. It is a figure (example 1) which shows typically the judgment method of the earliest heating start time (tsE). Same as above (Example 2). It is a figure which shows the hot water storage heat storage control flow in 3rd embodiment. 1 is a diagram illustrating a configuration of a conventional cogeneration system 100. FIG.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to FIGS. Needless to say, the scope of the present invention is described in the claims and is not limited to the following embodiments.

<First embodiment>
FIG. 1 is a diagram showing an overall configuration of a cogeneration system 1 according to an embodiment of the present invention. The cogeneration system 1 includes a fuel cell power generation unit 2, a hot water storage unit 3 including a hot water storage tank 4 and an auxiliary hot water heater 5, and a pipe group connecting these devices as main components.

  The power generation unit 2 includes a fuel processing device (not shown) that reforms natural gas in city gas into a gas mainly composed of hydrogen, and a fuel cell stack (not shown) that generates electricity by reacting the reformed gas and oxygen. 1), an inverter (not shown) that converts DC power obtained in the cell stack into AC power, an exhaust heat recovery device (not shown) that recovers heater heat generated by generated exhaust heat and surplus power, etc. Yes. City gas as fuel is supplied through a supply pipe 6.

The hot water storage tank 4 is configured to recover the generated power exhaust heat through the hot water circulation system 4 a by heat exchange with the exhaust heat recovery device of the power generation unit 2 and store the hot water in the hot water storage tank 4 as hot water. The hot water storage tank 4 is configured such that cold water corresponding to the amount of hot water consumed via the hot water supply pipe 4c is newly supplied via the water supply pipe 4b.
The auxiliary water heater 5 is configured to appropriately replenish the shortage of hot water in the hot water storage tank 4 by a heat storage control method described later. The auxiliary water heater 5 burns and heats the hot water in the hot water storage tank 4 circulated by the circulation pipe 5a and the circulation pump 5b to return to high temperature water (for example, 80 ° C.), and maintains the hot water storage tank 4 at the control temperature. It is configured as follows.
A plurality of temperature sensors (not shown) are arranged in the hot water storage tank 4 in the vertical direction, and the heat storage amount Q (t) can be measured based on the measurement of the hot water temperature of each part.

  The cogeneration system 1 is configured as described above. Next, a control flow in the present embodiment will be described with reference to FIGS. 2 to 3D. Operation control of the system 1 is performed by a control unit (not shown). In the following flow, in the “power generation schedule”, “waste heat recovery amount prediction”, and “hot water supply demand prediction”, a fuel cell operation control logic based on a known learning type algorithm (for example, JP-A-2006-266121) Based on the reference). Incidentally, in a commercially available actual machine, the current demand data is compared with the demand data of the same day of the past several months at the same time, and other parameters such as the water temperature are taken into consideration, and the closest date is extracted. Then, there is a method in which a demand pattern for 24 hours on the day is set as a predicted value for the next 24 hours, and a startup schedule is calculated based on this to determine an operation schedule.

With reference to FIG. 2, with the start of system operation, the power generation unit 2 is operated by load following control according to a predetermined power generation schedule. During operation, the generated heat is collected and stored on the hot water storage tank 4 side (S101). In the initial state, the heating operation by the auxiliary water heater 5 is not performed (q = 0) (S102). During the control, the heat storage amount Q (t) of the hot water storage tank 4 is always measured (S103), and when Q (t) is lower than the predetermined minimum heat storage amount Qmin (Y in S104), until it reaches Qmin or more. A heating operation at the maximum output qmax is performed by the auxiliary water heater 5 (S104b). If Q (t) ≧ Qmin (N in S104), the heating operation is performed with the heating output q = q (τ0) (S104a). The specific content of q (τ0) will be described later.
When a predetermined control update timing (t = t0) has been reached in this state (YES in S105), a heat storage amount prediction for n hours later is performed (S106, S107). For the predicted range n hours, the necessary time tb for boiling the hot water storage amount V of the hot water storage tank 4 from the normal temperature T0 to the set temperature TH (for example, 60 ° C., 80 ° C., etc.) with the auxiliary water heater 5.
tb = k · V (TH−T0) / qmax (1)
It is reasonable to set based on (where k is a unit of heat conversion).

The heat storage amount prediction is performed according to the following procedure. First, the hot water supply demand amount D (τi) and the exhaust heat recovery amount H (τi) in each time zone τi (i = 0 to n) from the current time t0 to n hours later (tn) are predicted (S106). In the following description. The correspondence between the time (ti) and the time zone (τi) is τ0 between t0 and t1, τ1 between t1 and t2, and τn between tn and t (n + 1).
Subsequently, the transition of the tank heat storage amount Q (ti) at the start of each time zone is obtained by the equation (2) (S107). In the same formula, heat dissipation from the hot water storage tank can body is small as compared with others, so it is ignored.
Q (t (i + 1)) = Q (ti) + [(H (τi) −D (τi)] (2)

Next, it is determined whether or not the heat storage amount Q (ti) at the start of each time zone is balanced with the hot water supply demand amount D (τi) in the time zone. The determination is performed in two stages, long time prediction and short time prediction (S108, S110). The short-term prediction means prediction based on the hot water supply demand amount D (τ1) in the latest time period τ1.
With reference to FIGS. 3A to 3C, an example in which 2 to 6 hours are set as the long-term prediction and 1 hour is set as the short-time prediction will be described here.
First, it is determined whether or not the hot water supply demand is satisfied in the long-time prediction (S108). Specifically, referring to the flow of FIG. 2A, the heat storage amount Q (ti) and the hot water supply demand amount D (τi) for the time zone τi (i = 2 to 6: after 2 hours to 6 hours). ) Difference ΔQ (ti) is obtained (S1081).
ΔQ (ti) = Q (ti) −D (τi) (2)
When ΔQ (ti) <0, it means that the hot water supply demand D (τi) in the time zone τi is larger than the heat storage amount Q (ti) in ti, and the heat storage amount is insufficient in the time zone τi. Will be caused. The insufficient heat storage amount at this time is represented by -ΔQ (ti).

Next, it is determined whether ΔQ (ti) <0, that is, the presence or absence of a time zone τi in which a shortage of heat storage is predicted (S1082). FIG. 3A shows an example in which ΔQ (ti)> 0 in all time zones. On the other hand, FIG. 3B is an example in which ΔQ (t5) = Q (t5) −D (τ5) <0 in the time zone τ (5).
If there is a time zone τi corresponding to ΔQ (ti) <0 (Y in S1082), and the water heater operation is started after the next update timing (t = t1), the maximum of the water heater Even if the heating operation is performed at the output qmax, the heat storage amount is insufficient, that is,
−ΔQ (tk)> qmax · (tk−t1) (3)
It is determined whether or not there is a time zone τk (k = 2 to 6) (S1083).

If there is a time zone τk corresponding to this (Y in S1083), it is not possible to satisfy the shortage of heat storage if the water heater is started after the next update timing (t = t1). In other words, it is necessary to operate the water heater from the current time zone t0 in order to satisfy the insufficient heat storage amount in the time zone τk.
Further, for each corresponding time zone τk, the water heater output q (k) necessary for satisfying the respective heat storage shortage is calculated by the following equation (4) (k = 2 to 6) (S1084).
q (k) = − ΔQ (tk) / (tk−t0) (4)
Further, the maximum values of q (k) and q (1) are determined and set as the water heater output q (τ0) (S1085). In addition, q (1) is a hot water heater output required in order to satisfy the heat storage shortage amount after 1 hour, and is represented by the following formula. When ΔQ (t1) ≧ 0, q (1) = 0 is considered.
q (1) = − ΔQ (t1) / (t1−t0)
Thereafter, returning to the flow of FIG. 2, the heating operation by the auxiliary water heater 5 is performed with the heating output q (τ0) obtained by the following equation (S109).
q (τ0) = Max (q (1), q (k))

If NO in S108, that is, if the hot water supply demand is satisfied in the long-time prediction, the determination by the short-time prediction is further performed (S110).
In the case of FIG. 3A and FIG. 3B described above, since the heat storage amount Q (t1) ≧ D (τ1) at the start time t1 of the time zone τ1, it is determined that the hot water supply demand is satisfied. In this case, no heating operation is performed by the auxiliary water heater 5 (S112).

On the other hand, in the case of FIG. 3C, the heat storage amount Q (t1) <D (τ1) is satisfied, so that it is determined that the hot water supply demand cannot be met. In this case, the heating operation is performed by the auxiliary water heater 5 so as to ensure Q (t1) ≧ D (τ1) by the start time t1 of the time zone τ1 (S111). A difference ΔQ (t1) between the heat storage amount Q (t1) and the hot water supply demand amount D (τ1) in the time zone τ1 is expressed by the following equation.
ΔQ (t1) = Q (t1) −D (τ1)
The heating output q (τ0) of the water heater in this case is
q (τ0) = − ΔQ (t1) / (t1−t0) (4) ′
Adjusted to

FIG.3 (d) is the figure which showed the thermal storage amount transition by a heating driving | operation compared with the case where there is no heating. In the figure, A (broken line) and B (solid line) indicate transitions of the heat storage amount when there is no heating operation by the water heater 5 and when there is, respectively. It can be seen that the heat storage (= Q ′ (t1)) for satisfying the hot water supply demand D (τ1) in the time zone τ1 is completed at the time t1 by the heating operation. In this case, by the heating output q (τ0) of the expression (4) ′ by the start time t1 of the time zone τ1,
−ΔQ (t1) = D (τ1) −Q (t1) = Q ′ (t1) −Q (t1) (4) ”
Will be stored.
By performing the above control at every predetermined update timing, the heat storage amount corresponding to the hot water supply demand can be constantly maintained.

In the present embodiment, an example in which a fuel cell is used as the power generation device has been described.
Moreover, in the transition prediction (equation (2)) of the tank heat storage amount Q (ti) in each time zone, the exhaust heat recovery amount H (τi) is included, but is corrected by updating every predetermined time (S105). Therefore, if the exhaust heat recovery amount is sufficiently small with respect to the hot water heater capacity (for example, 1/10), the exhaust heat recovery amount H (τi) may be omitted.

  Further, in the present embodiment, an example of one hour as a unit of time zone is shown, but it is also possible to adopt a mode in which updating is performed in units of shorter time (eg, 30 minutes, 10 minutes).

<Second Embodiment>
Next, another embodiment of the present invention will be described with reference to FIGS. Since the configuration of the present embodiment is the same as that of the first embodiment, redundant description is omitted.
With reference to FIG. 4, the control flow in this embodiment is as follows. The processes up to S201-S204b are the same as S101-S104b of the first embodiment. ). Note that q (τ0) in S204a is q (τ0) = 0 (when q = 0 at the previous determination) or q (τ0) = qmax (when q = qmax at the previous determination).

  When the predetermined control update timing (t = t0) is reached in this state (YES in S205), the heat storage amount prediction is performed until n hours later (S206, S207). Next, in order to complete the heat storage of the tank heat storage amount Q (ti) in each time zone by the start time ti of the time zone, a time ts (i) at which heating should be started retroactively is obtained (S208). Further, the time (tsE) closest to the current time (t0) among each ts (i) is determined (S209). In the case of FIG. 5, ts (4) corresponds to the closest time tsE in the case of FIG. 6, and ts (3) respectively. Further, it is determined whether or not the closest time (tsE) <time t1 (S210). If applicable (FIG. 5), the maximum output of the water heater 5 from the closest time (tsE) between t0 and t1. The heating operation at qmax is started (S211). In S210, when tsE ≧ t1 (FIG. 6), the process returns to S203, and the measurement of the tank heat storage amount Q (t) is continued at any time.

<Third embodiment>
Furthermore, another embodiment of the present invention will be described. This embodiment is different from each of the above-described embodiments in that not only the hot water storage tank heat storage amount Q (ti) at the time ti exceeds the hot water supply demand D (τi) in the latest time zone, but also for a plurality of time zones ahead. Is to operate the water heater so as to secure the required amount of hot water supply ΣD (τj) (j = i to i + m). Here, the example which heat-stores the predicted demand amount for 6 hours is demonstrated.

Since the configuration of the present embodiment is also the same as that of the first embodiment, redundant description is omitted.
With reference to FIG. 7, the control flow in this embodiment is as follows. The processes from S301 to S305 are the same as S101 to S105 in the first embodiment.
When the update timing t = t0 is reached, the prediction calculation of the hot water supply demand amount D (τi) and the exhaust heat recovery amount H (τi) (i = 0 to 11) is extended by 5 hours to τ11. It performs (S306).

Next, the transition of the heat storage amount Q (ti) at the start time t1 of the next time zone is obtained from the equation (5) (S307). In the same formula, heat dissipation from the hot water storage tank can body is small as compared with others, so it is ignored. Moreover, the prediction calculation of the tank heat storage amount Q (ti) is performed only from t1 to t6, and does not need to be performed after t7.
Q (t (i + 1)) = Q (ti) + [(H (τi) −D (τi)] (5)

Furthermore, the hot water supply demand total value ΣD (τi) between Q (ti) and ti˜t (i + 5) is compared (S308).
ΣD (τi) = D (τi) + D (τ (i + 1)) + D (τ (i + 2)) + D (τ (i + 3)) + D (τ (i + 4)) + D (τ (i + 5))
When Q (ti) ≧ ΣD (τi) is satisfied in all time zones i = 1 to 6 (Y in S308), the current state is continued until the next update timing.
If Q (t1) <ΣD (τi) (N in S308), the heating operation of the water heater 5 is performed so as to satisfy the heat storage shortage at the latest before the start of the time period (S309). The water heater output q in this case is the same as in the first embodiment S108-S113.

  By performing the above control at every predetermined update timing, the set hot water supply demand for a plurality of hours can be stored in advance, and the risk of hot water shortage when the hot water supply demand prediction is lost can be eliminated as much as possible.

  The present invention can be applied not only to a cogeneration system but also to heat storage control of an electric water heater, a heat pump water heater, or the like.

DESCRIPTION OF SYMBOLS 1 ... Cogeneration system 2 ... Fuel cell power generation unit 3 ... Hot water storage unit 4 ... Hot water storage tank 5 ... Auxiliary water heater D ... Hot water supply demand H ... Power generation waste heat recovery amount Q ... Hot water storage tank heat storage amount q ... Auxiliary water heater heating output

Claims (6)

In a cogeneration system equipped with a hot water storage tank that stores generated exhaust heat as hot water in a hot water storage tank, and a backup water heater for replenishing the shortage of heat storage amount,
Prediction of the balance between the amount of heat storage and hot water supply demand in each time zone τi (i = 0 to n) belonging to the predetermined prediction target time zone (t0 to tn), and shortage before the start of the time zone where shortage is predicted The backup water heater is operated to complete the heat storage ,
(A) For each time zone τi (i = 0 to n) from the current time (t0), based on the prediction of hot water supply demand D (τi) and power generation exhaust heat recovery amount H (τi), A step of obtaining a hot water storage tank heat storage amount Q (ti);
(B) For each time period, determining a supply and demand balance between the hot water supply demand D (τi) and the hot water storage tank heat storage Q (ti);
(C) any of the time zones in (τj), when the hot water storage tank heat storage amount Q (tj) is below the hot water demand D (τj) of the time period, those said time period starting just before the Q (tj ) Performing a heating operation of the backup water heater so as to maintain ≧ D (τj);
(D) repeating the steps (a) to (c) every predetermined update time;
A hot water storage control method for a cogeneration system, characterized by comprising: Instead of the steps (b) and (c),
(E) For each time zone, the hot water storage tank heat storage amount Q (ti) and the hot water supply demand total ΣD (τk) (k = i to i + m) for the subsequent multiple time zones (τi to τ (i + m)) Determining a supply-demand balance;
(F) In any time zone (τj), the hot water storage tank heat storage amount Q (tj) is the total hot water supply demand amount ΣD (τk) (k = j) for the subsequent multiple time zones (tj to t (j + m)). ~ J + m), the step of performing the heating operation of the backup water heater so as to ensure Q (tj) ≧ ΣD (τk) at the latest before the start of the time period,
The hot water storage control method of the cogeneration system according to claim 1 , comprising: In the step (c), when the hot water storage tank heat storage amount Q (t0) at the start of the latest time period (τ0) is lower than the hot water supply demand D (τ0) in the time period, the maximum of the backup water heater Heating operation with output qmax,
The hot water storage control method of the cogeneration system according to claim 1 . In the step (c), when there are a plurality of time zones in which the hot water storage tank heat storage amount Q (ti) is lower than the hot water supply demand amount D (τi), the backup water heater performs the heating operation at the maximum output qmax. Sometimes start at the start time of the time zone that should start
The hot water storage control method of the cogeneration system according to claim 1 . The hot water storage for a cogeneration system according to any one of claims 1 to 4 , wherein the prediction target time zone is a time required for the hot water storage tank to be fully stored only by the backup water heater. Thermal storage control method. During the control, when the hot water storage tank heat storage amount Q (t) falls below a predetermined minimum heat storage amount Qmin,
The hot water storage / storage control of the cogeneration system according to any one of claims 1 to 5 , wherein the heating operation of the backup water heater is given the highest priority until Q (t) ≥ Qmin. Method.

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