CN112668110A - Heat supply fuel cost apportionment method of gas-steam combined cycle cogeneration unit based on process division - Google Patents

Abstract

The invention discloses a heat supply fuel cost apportionment method of a gas-steam combined cycle cogeneration unit based on process division, which comprises the following steps: firstly, the combined cycle cogeneration is divided into two process flows of a gas turbine-a waste heat boiler-a steam turbine-a condenser and the gas turbine-the waste heat boiler-the steam turbine-a heat supply (a steam turbine part) and a heat supply (an original condenser part); then, calculating the improvement amount of thermodynamic cycle efficiency obtained by cogeneration based on the two extracted process flows; distributing the heat cycle efficiency improvement amount according to the proportion of the heat consumption of the steam turbine in the total heat consumption, namely the heat supply and the power generation, so as to correct the heat supply consumption; and finally, calculating the power generation heat consumption of the combustion engine, and calculating the cost sharing ratio of the heat supply fuel after merging the power generation heat consumption and the steam turbine heat consumption. The method can ensure that the heat supply enthalpy drop accounting for the sharing ratio is fully utilized, can encourage cogeneration enterprises to improve the production process, and can improve the utilization efficiency of external heat supply.

Description

Heat supply fuel cost apportionment method of gas-steam combined cycle cogeneration unit based on process division

Technical Field

The invention belongs to the technical field of cogeneration, relates to a method for reasonably distributing heat supply cost of a gas-steam combined cycle, and particularly relates to a heat supply fuel cost distribution method of a gas-steam combined cycle cogeneration unit based on process division.

Background

The gas-steam combined cycle fully utilizes the energy released from the high-temperature to low-temperature range of the flue gas, and effectively converts the heat into electric energy. The combined heat and power generation unit with the external steam supply further improves the heat efficiency of circulation, and provides a part of heat energy for external supply while generating electric energy. In this process, both heat and electricity play an important role: the electricity generation is indispensable and is a main product of a power plant; the heat production utilizes the heat of relatively low temperature low pressure for the unit thermal efficiency has obtained the promotion, does benefit to the heat user around simultaneously. However, the calculation of the heating cost still lacks a convincing scheme, the reasonable thermoelectric allocation ratio can effectively promote the reasonable utilization of energy, the enterprises can reasonably obtain the benefits brought by the improvement of the thermodynamic cycle efficiency, and the enthusiasm of the enterprises in improving the heating process and the overall cycle efficiency is improved.

Because the production form of the gas-steam combined cycle cogeneration is obviously different from that of the coal-fired cogeneration, no clear heat supply cost allocation method suitable for a gas-steam combined cycle cogeneration power plant exists at present.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a heat supply fuel cost apportionment method based on process division for gas-steam combined cycle cogeneration. In the invention, the flowing process of the working medium in the steam turbine at the downstream of the waste heat boiler of the gas-steam combined cycle cogeneration process is divided into a straight condensing unit and n back pressure type heat supply units (n corresponds to the steam extraction heat supply stage number of the steam turbine). The working process of the two units is divided into a steam turbine a and a steam turbine b according to the working medium, and in each back pressure type unit steam turbine b, the heat supply steam extraction flow D corresponding to each stage is provided_n,hThe working medium pushes the steam turbine b to generate electricity, then the working medium is pumped out to supply heat for heat users, and the enthalpy of the pumped steam is h_n,h(ii) a In the straight condensing unit steam turbine a, the flow rate is

The working medium directly generates power and enters a condenser.

The divided process flow can be seen in fig. 1 (taking n as an example, 1), the heat efficiency is improved due to cogeneration, and compared with a non-cogeneration unit, the heat efficiency is improved because steam in a steam turbine b does not enter a condenser any more but is used for supplying heat to heat users. Many methods exist in the field of coal-fired cogeneration (e.g. heat method, heat discount)A method,

Analytical methods, energy level methods, etc.) are not allocated based on the direct factor, which is one of the main reasons that the existing coal-fired cogeneration heat supply allocation method cannot be applied to the gas-steam combined cycle cogeneration process. Thermodynamic cycle efficiency boost Q_LThe expression of (a) is:

wherein n represents the number of steam extraction and heat supply stages, D_n,hHeat supply for n-th stage steam extraction, h_cIs specific enthalpy of exhaust steam, h_hSpecific enthalpy of condensed water of the condenser;

having obtained the cycle efficiency boost, consideration is given to attributing this portion of the boost, i.e., the portion of the efficiency boost that needs to be distributed among both thermal and electrical products. Firstly, calculating 1 to n enthalpy drop amounts for power generation of the steam turbine, namely enthalpy drops of power generation in n backpressure units:

wherein h is₀Is the specific enthalpy of the main steam, h_n,hThe nth-stage extraction specific enthalpy;

and secondly, calculating the enthalpy drop amount of the (n + 1) th part for power generation of the steam turbine:

and finally, calculating the enthalpy reduction amount of the extracted steam heat supply, namely the heat supply amount:

wherein h'_n,hThe specific enthalpy of the nth-stage heating backwater is provided;

from the above calculations and process divisions, Q_E,1，Q_E,2，Q_aThe heat directly consumed by the power generation at the steam turbine side from 1 part to n parts, the power generation at the steam turbine side from n +1 part and the heat supply respectively represents the energy consumed by the superheated steam generated by the waste heat boiler after entering the steam turbine in the combined cycle process to generate heat and electricity. In the process, the generated electric energy and heat energy are both opposite to Q_LHas an influence on the amount of Q, thereby_E,1，Q_E,2，Q_aAll need to participate in pair Q_LThe allocation of (c). According to the ratio, the cycle efficiency increase amount brought by heat supply is calculated and deducted from the heat supply amount, and the corrected heat supply enthalpy decrease amount of the steam turbine side can be obtained:

wherein eta_hrFor the heat exchange efficiency of the exhaust-heat boiler

As above, the enthalpy drop for power generation on the turbine side is calculated:

upstream of the turbine, the combustion engine is a device completely used for generating power, and the enthalpy drop amount can be calculated by subtracting the heat of exhaust smoke from the combustion heat of consumed gas:

Q_gt＝D_ngLHV_ng-D_gash_out (7)

wherein D_ngFor gas flow, LHV_ngIs natural gas low calorific value, D_gasIs the flue gas flow rate, h_outIs specific enthalpy of flue gas;

in addition, the situation that the waste heat boiler directly extracts steam for supplying heat can exist, and the situation is unrelated to a steam turbine, so that the part of heat does not participate in the distribution of the heating power cycle efficiency improvement amount and is only taken as the heat supply amount:

wherein D_i,DFor the ith flow supplied directly by the waste-heat boiler, h_i,DIs corresponding specific enthalpy of heat supply, h'_i,DThe corresponding specific enthalpy of the heating return water;

combining the upstream combustion engine side enthalpy drop and the downstream steam engine side enthalpy drop, the heat supply fuel cost sharing ratio is as follows:

the invention has the beneficial effects that:

the invention carries out scientific flow division on the gas-steam combined cycle combined heat and power cogeneration process flow, and obtains the heat supply cost sharing ratio on the basis of the flow division. Invention pair Q_E,1，Q_E,2，Q_aThe calculation of the method adopts the primary input quantity (namely heat supply extraction specific enthalpy, waste heat boiler heat exchange efficiency and return water enthalpy) in the parameters of the steam turbine and the waste heat boiler instead of the receiving quantity of the user side (namely heat supply steam specific enthalpy and condensate water enthalpy received by the user side). By adopting the method, the heat supply enthalpy drop accounting for the share ratio can be fully utilized, the cogeneration enterprises can be encouraged to improve the production process, the utilization efficiency of the external heat supply can be improved, the steam extraction parameters can be more actively reduced, the power generation capacity can be improved, and the integral gradient utilization efficiency of the combined cycle can be improved.

Drawings

Fig. 1 is an abstract view of a gas-steam combined cycle power generation with heat supply according to the idea of the present invention (the number of extraction heating stages n is 1).

Detailed Description

The calculation parameters related to the invention are easy to obtain and have strong operability, and the specific implementation method is as follows. A method for calculating the cost share ratio of fuel for gas-steam combined cycle steam extraction and heat supply comprises the following steps of dividing a combined cycle cogeneration process into two process flows of a gas turbine-a waste heat boiler-a steam turbine-a condenser and the gas turbine-the waste heat boiler-the steam turbine-heat supply (a steam turbine part) -heat supply (an original condenser part); then, calculating the improvement amount of thermodynamic cycle efficiency obtained by cogeneration based on the two extracted process flows; distributing the thermodynamic cycle efficiency promoting amount between heat and electricity according to the proportion of the heat consumption of the steam turbine in the total heat consumption, namely the heat supply and the electricity generation, so as to correct the heat supply consumption; and finally, calculating the power generation heat consumption of the combustion engine, and calculating the cost sharing ratio of the heat supply fuel after merging the power generation heat consumption and the steam turbine heat consumption. Taking a certain unit as an example:

thermodynamic cycle efficiency improvement:

44.19x(2276.4-83.74)/3.6＝26914.9kw

the heat supply enthalpy drop of the backpressure branch is as follows:

44.19x(3052.3-83.74)/3.6＝36439.1kw

the enthalpy drop of the back pressure branch circuit power generation:

44.19x(3365.5-3052.3)/3.6＝3844.5kw

pure condensing branch power generation enthalpy drop:

(122.09-44.19)x(3365.5-2276.4)/3.6＝23567.0kw

engine-side enthalpy drop amount:

22819x34047/3600-762.3x560.6/3.6＝97103.6kw

directly supplying heat enthalpy to reduce the quantity:

5.81x(2988.5-83.74)/3.6＝4688.0kw

the corrected enthalpy drop of the steam turbine is as follows:

[36439.1-36439.1/(36439.1+3844.5+23567.0)x26914.9]/0.99＝21291.9kw

the corrected enthalpy drop of the steam turbine is as follows:

[3844.5+23567.0+36439.1/(36439.1+3844.5+23567.0)x26914.9]/0.99＝43203.6kw

the cost sharing ratio of the heat supply fuel is as follows:

(21291.9+4688.0)/(43203.6+97103.6+21291.9+4688.0)＝0.156。

Claims (2)

1. a heating fuel cost sharing method of a gas-steam combined cycle cogeneration unit based on process division is characterized in that the combined cycle cogeneration is divided into two process flows of a gas turbine-waste heat boiler-steam turbine-condenser and the gas turbine-waste heat boiler-steam turbine part heating-original condenser part heating; then, calculating the improvement amount of thermodynamic cycle efficiency obtained by cogeneration based on the two extracted process flows; distributing the heat cycle efficiency improvement amount according to the proportion of the heat consumption of the steam turbine in the total heat consumption, namely the heat supply and the power generation, so as to correct the heat supply consumption; and finally, calculating the power generation heat consumption of the combustion engine, and calculating the cost sharing ratio of the heat supply fuel after merging the power generation heat consumption and the steam turbine heat consumption.

2. The heat supply fuel cost sharing method based on process division for the gas-steam combined cycle combined heat and power generation unit according to claim 1, characterized by comprising the following steps:

1) according to the steam extraction and heat supply stage number n of the steam turbine, the combined cycle is abstractly divided into n +1 parts, wherein the 1 st to n parts of working media generate electricity in the steam turbine firstly and then are extracted for heat supply, and the flow of each part corresponds to the steam extraction and heat supply D of each stage_n,hThe n +1 part only enters a condenser after generating power in a turbine;

2) calculating the improvement amount of thermodynamic cycle efficiency, wherein the total amount is the condensate gas loss corresponding to the steam extraction heat supply amount of the 1 st to n th steam turbines which originally enter the condenser

Wherein n represents the number of steam extraction and heat supply stages, D_n,hHeat supply for n-th stage steam extraction, h_cIs specific enthalpy of exhaust steam, h_hSpecific enthalpy of condensed water of the condenser;

3) calculating enthalpy drop amount of 1 to n parts for steam turbine power generation

Wherein h is₀Is the specific enthalpy of the main steam, h_n,hThe nth-stage extraction specific enthalpy;

4) calculating the enthalpy drop of the (n + 1) th part in the steam turbine

5) Calculating the enthalpy drop of the extraction steam supply

Wherein h'_n,hThe specific enthalpy of the nth-stage heating backwater is provided;

6) calculating the corrected enthalpy drop for heat supply at the steam turbine side

Wherein eta_hrThe heat exchange efficiency of the waste heat boiler is improved;

7) enthalpy drop for power generation on computer side

8) Calculating side enthalpy drop of combustion engine

Q_gt＝D_ngLHV_ng-D_gash_out (7)

Wherein D_ngFor gas flow, LHV_ngIs natural gas low calorific value, D_gasIs the flue gas flow rate, h_outIs specific enthalpy of flue gas;

9) the enthalpy drop amount of the direct heat supply by the waste heat boiler without passing through a steam turbine is calculated

Wherein D_i,DFor the ith flow supplied directly by the waste-heat boiler, h_i,DIs corresponding specific enthalpy of heat supply, h'_i,DThe corresponding specific enthalpy of the heating return water;

10) calculating heat supply fuel cost apportionment proportion

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