P rocedia CIRP 26 ( 2015 )735 – 739
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2212-8271 © 2015 The Authors. Published by Elvier B.V . This is an open access article under the CC BY-NC-ND licen (/licens/by-nc-nd/4.0/).
Peer-review under responsibility of Asmbly Technology and Factory Management/Technische Universität Berlin.doi: 10.1016/j.procir.2015.01.014
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12th Global Conference on Sustainable Manufacturing
Study of the Hydrogen-Steam Turbine Composite Cycle
Wu Weiliang *, Zang Shusheng, Zhong Ce
School of Mechanical Engineering, Shanghai Jiaotong University, DongChuan Road 800, Shanghai 200240, China
* Corresponding author. Tel.: 86-21-138********; fax:86-21-34206103. E-mail address : wuwl@
Abstract
It is propod a new type of the thermodynamic cycle in this article. The cycle is mainly compod by Hydrogen Generator (HG), Hydrogen Turbine (HT), Hydrogen-Oxygen Combustor (HOC) and Steam Turbine (ST). The pure hydrogen is generated in HG at high pressure and is heated up. The hydrogen with high pressure and high temperature develops power by flowing through HT. The hydr
ogen pasd through HT is burned with pure oxygen in HOC, and the generated steam provides power by expansion in ST quentially. Different from the conventional Combined Cycle (CC), this thermodynamic cycle is ries-wound by hydrogen turbine and steam turbine. Bad on the features this cycle is called as the Hydrogen-Steam Turbine Composite Cycle (HSTCC) in this article. It is indicated that HSTCC has a higher efficiency. It should
be a competitive power generating system using the sophisticated turbine technique for hydrogen energy in future. © 2014 The Authors. Published by Elvier B.V. Peer-review under responsibility of Asmbly Technology and Factory Management/Technische Universität Berlin. Keywords: Thermodynamic Cycle, Hydrogen Energy, Hydrogen Turbine, Steam Turbine.
Nomenclature
K thermal cycle efficiency HT W power generated by HT ST W power generated by ST 2H Q combustion heat of hydrogen in HOC 1. Introduction
World energy consumption is greatly growing with the
progress of civilization and society. Energy supply has
become the fundament of existence and development of
society. The large scale consumption of fossil fuels caus the
rious environmental pollution and social problems. It is
urgent to find a new types of energy and consuming
technologies that free human from the environmental
pollution. As energy carrier, hydrogen has outstanding
advantages in this aspect and is given more expectations [1].
For the mobile and distributed energy system, the pollution
can be considerably reduced by utilization of hydrogen [2].
The hydrogen belongs to condary energy, the mass
production of hydrogen and power generation by hydrogen
can control the pollution emission in a small area. How
efficiently to generate power by hydrogen becomes a key
technology accordingly. Many rearchers have investigated the novel strategy for consuming the hydrogen, for example
the fuel cell technique [3]. Technologies of traditional power generation, such as turbine and internal-combustion engine, are sophisticated and have been accumulated the rich experience in practical engineering. In order to minimize the
rearching and producing cost many rearchers have carried out the investigation for efficiently transforming the chemical
energy of hydrogen using the traditional technologies[4][5]. Due to the peculiarity of turbine engine, rearchers have
studied the application of gas turbine fueled by hydrogen in
ship [6]. Or using the gas turbine as key component, a variety
of advanced power cycle can be built up [7][8]. And the
cycle can be efficiently operated in a clean power generation
through CO2 capture and/or NOx elimination [9].
As the potential energy carrier for future, the hydrogen can
be produced by various methods [10][11]. Some of the
methods can be ud to produce the pure hydrogen, for
example the water photolysis pool or the thermal
decomposition furnace. Such unit is called as the hydrogen
generator (HG) in this article.
It is propod a new type of thermal cycle using turbine
technology bad on the concept of HG in this article. In this
propod cycle the water photolysis pool (PP) is ud as HG.
There are a gas turbine (hydrogen turbine, HT) and a steam © 2015 The Authors. Published by Elvier B.V . This is an open access article under the CC BY-NC-ND licen (/licens/by-nc-nd/4.0/).
Peer-review under responsibility of Asmbly Technology and Factory Management/Technische Univ
ersität Berlin.
736 W u Weiliang et al. / P rocedia CIRP 26 ( 2015 ) 735 – 739
turbine (ST) in the cycle, but different from CC, the HT is
connected with steam turbine in ries. In the HT and ST the solar energy collected by process in HG will be transformed into thermal and mechanical energy in combustor and turbines efficiently. It is showed that the cycle has high efficiency without pollution. It provides an optional cycle technique for hydrogen power generation in future. 2. Layout of the proposal thermal system
It is shown the layout of the propod cycle in Figure 1. The cycle consists of Feed Pump (FP), Hydrogen Generator (HG), Hydrogen Heat Exchanger (HHE), Hydrogen Turbine(HT), Hydrogen-Oxygen Combustor (HOC), Steam Turbine (ST), Condenr (Cd), Condenr Pump (CP) and Feed pump (FP). During the cycle operating, water is firstly pressurized by the FP. The pressurized water is decompod into hydrogen and oxygen by sunlight in HG. Then the hydrogen enters in the HHE and be heated, and the energy for heating the hydrogen is come from the HOC. After that the hydrogen will firstly expand and generate power in the HT. The in HT expanded hydrogen will then enter into the HOC
and combust with pure oxygen from the PP. Part of the energy produced in combustion will be ud to heat the hydrogen in the HHE. Becau the temperature of steam, the product of the combustion product of pure hydrogen-oxygen, is very high, the steam must be cooled by using the liquid water so that the material of the turbine can suffer the high temperature. Thereafter the steam will expand quentially and generate power in the ST. The steam exhaust will finally conden into water in the Cd. And the condend water will be pumped by the pump in the CP and HOC proportionally. After the process the cycle is completed.
In the above mentioned cycle, the components before the HT constitute the top cycle and that after the HOC constitute the bottom cycle. It can be concluded that the propod cycle us sunlight as the energy and combined with sophisticated technologies of gas (hydrogen) and steam turbines. The high grad energy can be utilized in HT and that of the low grad will be utilized in ST contrarily. So the cycle accords with the cascade utilization principle of thermal energy and should have higher efficiency. Becau the HT and ST are rially connected in the propod cycle, it is named as Hydrogen-Steam Turbine Composite Cycle (HSTCC) especially.
Figure 1 Layout of the HSTCC system
3. Evaluation Result and Discussion 3.1. Evaluation Result of HSTCC
There is no evaluation method for the propod cycle efficiency at prent. To analyze performance of this it is treated as below:
Taking 1kg water entered in HG for example, the enthalpy of the substance from this 1kg water at different period in the HSTCC is calculated. Becau there are two units outputting power in the HSTCC, so the cycle efficiency is defined by: 2
HT ST
H W W Q K
(1)
HT W , ST W and 2H Q can be calculated according to the
relevant theory.
The maximal temperature in a thermal cycle is the most important parameter for efficiency. The combustion heat of pure hydrogen and oxygen is so tremendous that no materials can be suffered the temperature of the combustion product without cooling. So the generated steam in the HOC must be firstly cooled with coolant. Considering the feature of the cycle it is suitable to u water as the coolant. According to the prent technology and possible progress in future, it is assumed that the highest temperatures in the cycle equals to 1673.15K in evaluation. The temperature in other components is shown as follows:
The water is decompod to pure hydrogen and oxygen by photolysis in the HG and the temperature of the decompod pure hydrogen and oxygen equals to 293.15K. The hydrogen entere
d in HHE will be heated to a certain temperature, and the highest temperature is assumed to 873.15K in this article. In HOC the water at 293.15K is ud to cool the combustion
Steam Water
O 2
H 2
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W u Weiliang et al. / P rocedia CIRP 26 ( 2015 )735 – 739
product and the highest temperature of stream at the HOC
outlet equals to 1673.15K. The pressure at ST outlet is t to
8.5kPa according to the steam turbine power plant
specification. This pressure corresponds to the temperature of
315.84K in condenr.
Other parameters for efficiency evaluation of the HSTCC
are summarized in Table 1.
Table 1. Parameters for Evaluation of HSTCC
FP K FP0.9 P FP50~150 T FP293.15
HG K HG0.02
T HG293.15
HHE K PHHE0.03
T HHE293.15~873.15
HT K HT0.88
P HTO10~30
HOC
WM Hydrogen/Oxygen K PHOC0.02
K C0.995
T HOC473.15~1673.15 T HOCW293.15
ST K ST0.88
P ST0.0085
Condenr P C0.0085
T C315.83
CP WM Water K FP0.9 T CP293.15
x WM: working medium
x TC: The temperature is corresponding to P c.
For evaluating the efficiency the hydrogen is treated as ideal gas and the steam property is referred t
o [12]. Recurring to simulation, the influence of different parameters to cycle efficiency is also investigated, such as the hydrogen recuperative temperature in HHE, and the temperature at HOC outlet.
Figure 2. The cycle efficiency versus the recuperative
temperature at HHE inlet
It is prented the curve of the cycle efficiency to the recuperative temperature of hydrogen at the HHE outlet in Figure 2. This curve is corresponding to following condition: water pressure of 100MPa at the FP outlet, hydrogen pressure of 10MPa at the HT outlet and steam temperature of 1673.15K at the HOC outlet. It is indicated that the highest cycle efficiency is 60.18% when the recuperative temperature of hydrogen equals to 392K. And the higher cycle efficiency can be achieved at the lower recuperative temperature of the HHE. It means that the comparative cycle efficiency can be obtained using the simple layout without the HHE. With another word, the HHE is be moved away from the HSTCC in order to simplify the system and decrea the building cost. Figure 3. Cycle efficiency versus temperature at HOC outlet It is shown the relation curve between the cycle efficiency and the steam temperature at HOC outlet in Figure 3. Other conditions are prented as fo
llowing: water pressure of 100MPa at the FP outlet, hydrogen pressure of 10MPa at the HT outlet and hydrogen recuperative temperature of 392K at the HHE. It is indicated that the cycle efficiency will increa with the steam temperature at the HOC outlet (i.e. ST inlet). The result is consistent with conventional understanding.
3.2.Discussion
At same temperature of 1673.15K the efficiency of the HSTCC is higher about 1% than that of the Humid Air Turbine (HAT). And compared with other power cycle with gas turbine, such as Combined Cycle (CC), HAT and Steam Injected Gas Turbine (SIGT), HSTCC can not only achieve the high efficient, but also has many other advantages: First, feed pump is ud as the stating part of HSTCC so that there is no loss caud by compressing air in gas turbine. Second,
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pure oxygen is ud for combustion, then the hydrogen turbine and the stream turbine can be connected in ries, the exhaust loss of the gas turbine in other kind of cycle will be vanished. The all can increa the efficiency of the HSTCC.
Both of the HT and ST generate power in HSTCC. The power generated by the HT will be affected by its pressure drop. Becau the HT and ST are connected in ries, the total pressure drop of the cycle equals the product of the pressure drop in HT and ST. Therefore the FP in HSTCC should have a strong boosting ability comparing to the compressor in the above mentioned cycles. The liquid water, which is easy to be boosted, is applied as the working medium in the FP, it is feasible to boost the water at high pressure ratio in practical engineering. The total generated power of the cycle is interconnected with the recuperative temperature of hydrogen in HHE. With poor recuperation at the HHE, the hydrogen temperature at HT outlet becomes lower, thus the generated power by the HT will have the decreasing trend. On the contrary, the energy which is transferred by H2 into the HOC will be incread with strong recuperation, the power output by the ST should have the incread tendency. Under the effect of the contradictory factors the cycle has an efficiency curve like Figure 2.
Figure 4 T-s curve of HSTCC
With increasing the temperature at the HOC inlet, the water for cooling the steam formed by combusting in HOC will be decread. Becau the specific enthalpy of the water in the condenr is constant, the efficiency will be rin with the temperature at HOC outlet as shown in Figure 3.
Becau the water at 293.15K is directly ud for cooling the steam with high temperature in HOC, so it will exist a large amount of the entropy loss. If the water as the coolant is recuperated at the appropriate location in the system, the cycle efficiency should be furthermore incread.
The working mediums in the HSTCC change constantly in its substance, amount and state. It is different from the traditional cycles for performance evaluation, in which the substance composition, amount is invariable, or barely unchangeable. To evaluate the cycle efficiency the unit mass (1 kg) of working medium in the starting component will be ud to analysis this composite cycle in T-s concept. If the working medium is reacted with another substance, the enthalpy of all reaction resultants will be ud for evaluating the cycle performance.
Bad on this analytic method, the hydrogen of an amount of 0.111kg produced from 1 kg water by photolysis will be investigated in HG. When a substance is added to the process of energy transformation from outside, such as oxygen and cooling water is added to HOC, the enthalpy of the total amount of the vapor will be simulated. So the amount of the working medium at different stage should be considered for evaluating the HSTCC. It is schematically shown the T-s curve of HSTCC according to the above mentioned method in Figure 4.
As shown in Figure 4, “1” means the liquid water of 1 kg in CP/FP. It is boosted by FP and translated to “2” and the temperature is raid. Becau of the incompressibility of water this temperature ri is ignored in this article. The photolysis process in HG is prented as “2” to “3”, it is considered as an isothermal process. “3” to “4” means the isobaric heating process of hydrogen in HHE, which has an amount of 0.111kg. “4” to “5” prented the intropic expansion of hydrogen of 0.111kg. “5” to “6” means the isobaric heating process in HOC, in which pure hydrogen and oxygen is combusted and injected water is evaporated for cooling the steam. In this stage the amount of working medium is greatly incread. “6” to “7” prents the intropic expansion process of steam in ST. ‘7’ to “1” prents the exothermic process at constant pressure of vapor in condenr. Thus it can be concluded that there is no exhaust loss in HSTCC compared to CC. It is beneficial to improve the efficiency of the cycle.
When the hydrogen turbine is introduced into the cycle, thermal process of HSTCC is much more clo to isothermal expansion. Therefore the increa of efficiency becomes a merited cour.
739 W u Weiliang et al. / P rocedia CIRP 26 ( 2015 )735 – 739
Bad on the same reason, other strategies, such as the heat recuperation, are introduced in the HSTCC, the efficiency should be father improved.
4.Conclusion
It is propod a new type of thermal cycle called as HSTCC in this paper. According to evaluation it c
an be concluded below:
x In comparison with CC, there is no exhaust-heat boiler and compression work in HSTCC. So this cycle has the advantages of the simple layout and higher efficiency.
x Except for HG, other components in HSTCC are sophisticated in technology. So the developing cost for the new thermal cycle is low.
x The HSTCC can u sunlight as sources of energy. And there are pure hydrogen and pure oxygen in combustor only, so no NOx can be formed during combustion. So it is an environment-friendly power generation technique.
x The thermal process of HSTCC is much more clo to isothermal expansion, so it has an expectant potential for increasing the efficiency.
Bad on the above advantage, the HSTCC should be a competitive power generating system using the sophisticated turbine technique for hydrogen energy in future.
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