THERMODYNAMIC OPTIMIZATION OF CYCLES
OF SOME SCHEMES OF GAS AND GAS-STEAM TURBINE POWER PLANTS WITH THE HELP OF
MODERN INFORMATION TECHNOLOGIES
10th conference on Power System
Engineering, Thermodynamics & Fluid Flow - ES 2011
June
16 - 17, 2011,
VOLOSHCHUK Volodymyr, OCHKOV
Valery, ORLOV Konstantyn
On the base of mathematical
modelling, with the use of the Mathcad Calculation Server technology the
examples of investigations of some cycles of gas and gas-steam turbine power
plant are given in the work. It is shown, that, on the whole, except for
existent methods (increasing gas turbine inlet temperature, optimization of
steam turbine inlet parameters, using multipressure steam generators, etc.),
the complication of gas and gas-steam combined cycles, namely intermediate compression with intercooling of
cyclic air and reheat in gas turbine cycle, allows to increase their efficiency.
Keywords: information
technologies, Mathcad
Calculation Server, gas and gas-steam combined power plants, efficiency.
Introduction
Prospect direction in power plants development is related with
gas-turbine (GTP) and gas-steam turbine (GSTP) power plants [1 - 3].
In general, ways of efficiency increase of GTPs GSTPs have not been
studied completely. This is a complex, multi-parameter problem which in many
cases can be solved by means of mathematical simulation.
Due to wide use of mathematical packages, such as Mathcad, Matlab,
Mathematica, Maple, and others, which came to take place of programming
languages, engineers specializing in thermal power engineering can solve
problems in a quick and efficient manner without the need to resort to the aid
of third-party programmers.
The first place in the list of the most important “IT-revolutions”
belongs to development of so-called “cloud computing” – providing of remote
computing ability, footprint (“clouds”) and communication channels for
customers. The reason which begets using of “cloud computing” is high cost for
program licenses for detached workstations, rent of space, electricity and
control of software piracy. By “clouds” we mean computing centers which are
significantly more powerful than user’s stationary infrastructure. Instead of
physical servers customers use virtual servers which are spread in allocated
net of computers with industrial ability.
2. Analysis of latest investigations
Investigations and analysis of
cycles of GTP and GSTP are given partially in works [1, 2, 3, 4, etc.]. But at
the same time, in our opinion, such power plants should be additionally
studied.
For example, in [2], when
investigating exemplary GTP and GSTP cycles some simplifications have been
done: multi-stage air compression and multi-stage heat addition in gas turbine
cycle were changed into isothermal processes which can not be realized in real
gas turbine power plant. In addition, in [2], gas turbine (GT) cooling was not
taken into account, which is obligatory to protect the hot turbine components
from excessive thermal stresses. In [1] cases of optimization of parameters of
steam turbine as a component part of GSTP were mainly considered. At the same
time optimization of parameters of GTP as a component of GSTP in the given work
were not practically studied. In addition, in [1] schemes of GSTP were
investigated at today’s level of development and possibilities of power
mechanical engineering. Possibilities of GSTP
development in future due to cycles complication of such units are not analyzed
enough in [1].
Specialists of Moscow Power
Engineering Institute (Technical University) with participation of research
workers of other organizations have created a website located at www.vpu.ru/mas which can be useful for all who
need to determine properties of working fluids or heat carriers and
mathematical simulations or visualization of processes in power engineering
[5].
Results of investigations and analysis of different schemes of GTPs
and GSTPs can be found in specialized
literature. But such sources are not always easily accessible and they often
give only partial information.
3. Task setting
Therefore the given paper provides information regarding investigation
and analysis of some schemes of gas-steam combined cycles via the website http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html in an interactive mode with the
purpose of optimization of such power units.
4. Presentation of the main material
Figure 1 shows the page of the website http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html where a user can see a list of types of power units which can be numerically investigated in an interactive mode.
.
Fig.
1: Fragment from a website http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html
where it is possible to do numerical investigation of thermodynamic cycles of
power units in an interactive mode
Theoretical investigations of
influence of multi-stage air compression and multi-stage heat addition in GTP
and GSTP cycles on the efficiency of GTP and GSTP are presented in [6]. Using
these results numerical simulation will be provided in this paper.
According to [6] a high efficiency of
gas-steam combined cycles can be theoretically received if reheat and
intercooling is applied.
An example of input data block which
is prepared according to the technology of Mathcad Calculation Server –
technology which allows to post Mathcad worksheets in Internet so that a user
can fill in interactive math calculation forms without having to know or own
Mathcad – is shown in Figure 2.
Fig. 2: Input data
block prepared on technology of Mathcad Calculation Server for numerical
simulation of GSTP
Therefore,
a user of the site http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html chooses required source from the list (Binary cycles),
fills in input data which are located in special “live” cells, presses button
“Recalculate” and receives calculated data about characteristics of the chosen
thermodynamic cycle.
In
the given paper, for an example, there were made calculations for schemes of
GSTP in which gas turbine inlet temperature was 1200 oC. In a case
of GSTP with multi-stage air compression there were three compressors:
respectively low-pressure compressor (LPC), middle-pressure
compressor (MPC), high-pressure compressor (HPC). In a case of GSTP with
multi-stage heat addition there were two or three gas turbines: respectively high-pressure
turbine (HPT) middle-pressure turbine (MPT) and low-pressure turbine (LPT).
In
the figure 3 results of numerical simulation of the chosen schemes of GSTP
plants are shown.
Fig. 3: Results of numerical
simulation of the influence of GSTP cycle complication on efficiency of GSTP;
gas turbine inlet temperature is 1200 oC; compression
ratio in LPC and MPC is 1,2;
expansion
ratio in HPT and MPT is 3: 1 - GSTP consists of
GTP with one-stage air compression, one-stage heat addition and single-pressure
heat recovery steam generator (HRSG) with reheat; 2 - GSTP consists of
GTP with one-stage air compression, one-stage heat addition and double-pressure
HRSG with reheat; 3 - GSTP consists of GTP with one-stage air
compression, two-stage heat addition and single-pressure HRSG with reheat; 4 - GSTP consists of
GTP with three-stage air compression, two-stage heat addition and
single-pressure HRSG with reheat; 5 - GSTP consists of
GTP with one-stage air compression, two-stage heat addition and double-pressure
HRSG with reheat; 6 - GSTP consists of
GTP with three-stage air compression, two-stage heat addition and
double-pressure HRSG with reheat; 7 - GSTP consists of
GTP with one-stage air compression, three-stage heat addition and
single-pressure HRSG with reheat; 8 - GSTP consists of
GTP with three-stage air compression, three-stage heat addition and
single-pressure HRSG with reheat
So,
first of all, lines in figure 3 which correspond to single-pressure HRSG are
limited to some values of general compression ratio. That is conditioned by the
technological requirements for GSTPs. The extreme left points of these lines
correspond to the minimum value of compression ratio for which the exhaust
gases temperature after HRSG has the minimum value – 70 oC (for the
line 3 in the figure 3 that corresponds to compression ratio of
). The extreme right points of these lines correspond to the
maximum value of compression ratio for which temperature difference between
inlet exhaust gases and outlet superheat steam is decreased to 20 oC
(for the line 3 in the figure 3 that corresponds to compression ratio of 
). Moreover, in the figure 3 it is shown that for some values
of general compression ratio lines for double-pressure HRSG are absent – there
is no reason to use it. On the other hand, lines for single-pressure HRSG for
these values of general compression ratio are presented. For GSTP which
consists of GTP with one-stage air compression and two-stage heat addition
(line 5 in the figure 3) using double-pressure HRSG is not reasonable when
values of general compression ratio are from 15 to 30 because single-pressure
HRSG can completely utilize the heat of exhaust gases (in the figure 4 thermal
diagram of such HRSG is shown with continues lines). That takes place because
when decreasing 
exhaust gases
temperature after GTP is increased and for 
, according to heat and mass balances of HRSG, steam
generation is high enough for single-pressure HRSG to utilize the heat of
exhaust gases.
It
should be noted that according investigations presented in [6], maximum values
of efficiency of GSTP with multi-stage air compression, heat addition and
single-pressure HRSG (lines 3, 4, 7 and 8 in figure 3) corresponded to cases
when transition of minimum temperature difference between gases and water from
one end of economizer to another takes place. For example, for schemes which
correspond to lines 3 and 4, when 
, minimum temperature difference in HRSG takes place at cold
side of economizer (in the figure 4 the thermal diagram of such HRSG is shown
with continues lines). When 
, minimum temperature difference in HRSG passes to hot side
of economizer. In the second case it is reasonable to use double-pressure HRSG
(in the figure 4 the thermal diagram of such HRSG is shown with stroke lines).
The
figure 3 shows that, in general, multi-stage air compression and multi-stage
heat addition in HRSG can increase efficiency of such plant. For example, using
two-stage heat addition gives 5 % increase of HRSG’s efficiency in comparison
with one-stage heat addition (lines 1, 3 and 4 in the figure 3).
Using
three-stage heat addition gives another 3 % growth of HRSG’s efficiency in
comparison with two-stage heat addition schemes (lines 3, 4, 7, 8 in figure 3).
But it should be noted that schemes of GSTP with three-stage heat addition can
theoretically exist at high compression ratio (
). GTP plants with 
are installed
nowadays. But GTP plants with are not possible at
present level of power mechanical engineering.
It is
also shown in the figure 3 that using multi-stage air compression for
decreasing compression work is not an effective way for efficiency improving of
GSTP units analyzed in the paper.
Fig.
4: Thermal diagram of single-pressure HRSG:
continuous lines - 
; stroke lines 
Conclusion
Using a
mathematical package Mathcad for which a network publisher is Mathcad
Calculation Server allowed to create a website http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html that made possible to do interactively calculations of
thermodynamics cycles of thermal power installation.
Numerical
simulation of thermodynamics cycles of some schemes of GSTP made via the
website showed that besides ways which are often used nowadays efficiency
growth can also be reached by using multi-stage heat addition.
Using
multi-stage air compression for decreasing compression work is not an effective
way for efficiency improving of GSTP units analyzed in the paper.
Almost all
possible ways of improving efficiency need to increase the value of air
compression.
The
website http://twt.mpei.ru/ochkov/VPU_Book_New/mas/index.html is open for different purposes, which may include it being analyzed and
criticized, corrected for removing assumptions, extended for a wider range of
application, etc.
Literature
[1]
S. V. Tsanev and others. Gas Turbine
and Gas-Steam Turbine Power Units of Thermal Power Plants // M.: Publishing
House of MEI, 2006, 584 pp.
[2]
A. Andryushchenko.
The Thermodynamic Efficiency of Complex Cycles of Gas-Turbine Units in
Combined-Cycle Installations // Thermal engineering, 1998, Vol. 45, No. 3, pp.
68 – 71.
[3]
Kehlhofer, R., Combined-Cycle Gas & Steam Turbine Power
Plants, The
[4]
Gas
Turbine World 1997 Handbook, Pequot Publishing,
[5]
V.
F. OCHKOV, A. A. Aleksandrov, V. A. and others.
Caclulations of Thermodynamic
Cycles via Internet // Thermal engineering, 2009, Vol.
56, No. 1, pp. 86 – 89.
[6]
V. A. Voloshchuk. Thermodynamic
optimization of exemplary cycles of some schemes of gas and Gas-Steam Turbine
Power Plants // Vestnyk of NTU “HPI”, 2011, No. 6, pp. 77 – 87.
VOLOSHCHUK
V., National University of Water Management and Nature Resources Use,
Department of Heat and Mechanical Engineering, Soborna, 11, Rivne, 33028, Ukraine, Phone:
+3-8067-362-69-55, Email: Volodya-28@yandex.ru
OCHKOV
V., Moscow Power Institute (
Fuel
Technology on the thermal and nuclear power stations, Krasnokazarmennaya 14,
111250
ORLOV
K., Moscow Power Institute (
Fuel
Technology on the thermal and nuclear power stations, Krasnokazarmennaya 14,
111250