Estimation the conjugate pressure of fresh steam and steam behind intermediate superheating.

Parametric optimization of the heat schematic

(exersise by the book "Fundamentals of projecting of the heat schematic power generating unit of thermal power station, operating on the supercritical parametrs." Authors: Dorohov E.V., Sedlov A.S. Publishers MPEI, 2007)

Conjugate pressure of the fresh steam supports defined ultimate ratio of steam dryness in defined temperature of the fresh steam. Modifying the value of ultimate ratio of steam dryness, there is a possibility to find an optimal pressure of the fresh steam by criterion of an energetic efficiency of the heat schematic power generating unit. The more the steam dryness in CLP exchaust, the less abrasion and the high efficiency of the last step. In this case considering the heat schematic power generating unit with an intermediate superheating and two regenerative heaters. There are some statements of tasks. You should record results to the paper by hand.

Task 1.For definied steam parameters in the turbine exchaust (Pк, Xк), having condition of the constant pressure, you should find conjugate meaning parameters of the fresh steam and steam behind intermediate superheating using variation calculation by criterion of minimum specific fuel rate netto and electric power.

Task 2.For definied temperature of the fresh steam and intermediate superheating, you should find the value of ultimate ratio of steam dryness, while netto efficiency of the power generating unit has maximum. Minimum acceptable the value of ultimate ratio of steam dryness is 0.92.

Task 3.In which parameters of the fresh steam, the efficiency of the power generating unit will have maximum. Minimum acceptable the value of ultimate ratio of steam dryness is 0.92.

Basic data(considering task 1):

Steam rate, kg/s

Temperature of fresh steam , ⁰C

Steam temperature before gate-type valve of MPС , ⁰C

Steam dryness factor on the exchaust of LPС, pos.units

Pressure on the last step of LPС, MPa

Recommending pressure on the exchaust of MPС, MPa

Domestic comparative efficiency of HPС, MPС and LPС

Comparative loss of pressure in pressure enter body of HPС in reheat circuit, in insolating valves of HPС, in receivers of LPС, pos. units.

Mechanical and generator efficiency

Transport efficiency from steam boiler to turbine

Steam boiler brutto efficiency

Specific heat of fuel combustion

kJ/kg

Power rate of electric drive of blow fans and smoke exhausters,

(prototype: gasproof steam boiler TGME-206 4,87 kWt*h/Gkall)

Effective (total) efficiency of feeding pump

Effective (total) efficiency of condensate pump

Efficiency of electric drive pumps

Loss of pressure in a steam boiler, in pipelines of the fresh steam and feeding water, MPa

Loss of pressure in regenerative bleed-off lines, pos. units.

Underheating (temperature force) of regenerative heaters, ⁰C

Specific heat of combustion of equivalent fuel

kJ/kg

Loss of water pressure in regenerative heater, MPa

MPa

Pressure of condensate pump

MPa

Estimation of warm water in condensate pump, kJ/kg

Consumption of feedwater, kg/s

Calculation:

Complementary conditions and assumptions:

-Consumption of feedwater equals to consumption of fresh steam (without leaks);

-Pressure in the exchaust of LPC is constan;

-Comparative loss of pressure in reheat circuit is constan;

-The condenser pressure equals to pressure in the exchaust from the last step of the turbine;

-Losses with a slew rate in the exchaust of a turbine don't calculate;

-Change of electricity amount for drive circulating pumps does not calculate ;

Assumptions: p_{exch_turbine}=const, p_valve=const, h_oi = const

Condensate temperature and enthalpy of waste steam in the condensator exchaust:

MPC and LPC models for calculating of steam expansion process as a function of steam temperature

before shut-off valves of MPC having this temperature.

Using cycle statement for (but not while),we can refrain from "cycling" such calculation,

having irregulard basic data input.

HPC exchaust pressure

LPC entrance pressure

Functions of steam parameters the HPC expansion process

Steam enthalpy in the HPC exchaust, in case the expansion process realizes without energy losses (isoentropic process):

Steam enthalpy and entropy in the HPC exchaust

Exchaust pressure of feeding pump (FP) as a function of fresh steam pressure, MPa

Steam and condensate parameters in the regenerative heating system

Specific volume of a turbine condensate, CP heating and electric drive power of CP

Steam and condensate parameters in the heater case H1 and in the exchaust one

Steam and condensate parameters in the heater case H2 and in the exchaust one

Drainage enthalpy, pouring out from H2

Feedwater enthalpy after H2

This is a function-subprogram for calculating feedwater heating in the setting of feeding pump (FP) and this electric drive power

The function of the electric drive power of feeding pump, water enthalpy in the exchaust and water heating in the settings of feeding pump

Steam consumption in the regenerative heater H1

The function of steam consumption into regenerative heater H2, which depends on

unknown quantity pressure of fresh steam P₀, kg/s

The function of steam consumption through the steam boiler reheater and in MPC, which depends on

unknown quantity pressure of fresh steam P₀, kg/s

The function of steam consumption in LPC, which depends on unknown quantity pressure of fresh steam P₀, kg/s

Parametrs modelling of an energy efficiency

The function of heat consumption in the turbo-installation

The function of the heat fuel consumption in the steam boiler

The function of fuel consumption in the steam boiler

The function of the domestic power of turbine cylinders and electrical power of the power-generating unit

The function of estimation of an electrical power for drive smoke exhausters and blow fans, which depends on the heat fuel consumption in the steam boiler, kWt

Specific heat rate on the turbo-installation brutto, kJ/kWt*h

Power-generating unit efficiency for supplying electic output, pos. units

Specific rate of an equivalent fuel for supplying electic output, g.e.f./(kWt*h)

Starting value of the fresh steam for an optimization procedure, MPa

Search range of the optimal pressure of the fresh steam

The conclusion of the calculation results

The consuption of fresh steam

The generator terminal electric output

Associated pressure of the fresh steam

The steam pressure under the isolation valve of MPC

Specific rate of an equivalent fuel for supplying

electic output (netto)

Efficiency of the power-generating unit netto

Specific heat rate on the turbo-installation brutto

Steam dryness factor on the turbine exchaust

Exchaust pressure of feeding pump

Entropy of the fresh steam

Entropy of the steam on the first step HPC entrance

Entropy of the steam on the HPC exchaust

Enthalpy of the fresh steam

Enthalpy of the steam in the first step HPC entrance

Enthalpy of the steam on the HPC exchaust

Enthalpy of the steam on the LPC exchaust

The electric drive power of feeding pump

The electric drive power of drive smoke exhausters and blow fans

Steam consuption on the heater (H2)

Steam consuption on the heater (H1)

Steam consuption in the condenser

Conclusion:

Translated by Dmitrenko A.V.