Aminov R. Z., Bayramov A. N.

Department of Energy Problems of Saratov Scientific Center

of Russian Academy of Sciences

Investigation of the efficiency of Atomic power station in to integrate with energy complex with hydrogen fuel

Proposed a scheme of the energy complex with hydrogen fuel in to integrate with atomic power station. Evaluated technical and economic parameters of the hydrogen cycle depending on proportion used by off-peak power NPP power unit. Determined by the competitive efficiency of atomic power station with energy complex with hydrogen fuel in comparison with the pumped storage station.

Strategy for the Development of Atomic Energy of Russia envisages a substantial increase in the share of atomic power station in power systems of European part of Russia. In this connection, issues of improving the safety and effectiveness of their work are especially actual.

The planned high growth rates of the atomic power station leads to the problem of providing base-electrical-load during the period of nighttime lows in the electricity grid. Traditionally, to align of base-electrical-load of atomic power station supposed to use pumped storage station, but since their construction requires special environmental conditions and, as a rule, the near the NPP is not possible, this suggests that they be charging from the grid. In this case, the night the electricity tariff significantly exceeds the self cost of electrical energy of atomic power station, which significantly affects the cost of peak electricity produced by pumped storage plant. In this connection, a need to develop alternative technologies of accumulation of electricity. One such technology may be the use of energy complex with hydrogen fuel, the advantage is its location near a atomic power station with the possibility of charging at self cost of electrical energy. At night, carried out produce of hydrogen and oxygen by electrolysis of water and their accumulation in the storage system. In the hours of peak electrical load, hydrogen and oxygen are used in a cycle of atomic power station to increase its electric power.

Thus, development of efficient and reliable energy complex with hydrogen fuel is actual.

Energy complex with hydrogen fuel includes a water electrolysis system of high power and pressure, gas compression system before and after the storage capacity, a system of storage of hydrogen and oxygen on the basis of metallic storage capacity (in Fig. 1 for example, the steam turbine K-1000-60/1500).

Fig.1 – Schematic Diagram Of The Integration Of Atomic Power Station With Energy Complex With Hydrogen Fuel:

1 – water electrolysis system; 2 – a system of compressing hydrogen and oxygen; 3 – system of storage of hydrogen and oxygen on the basis of metallic storage capacity; 4 – final cooling heat exchanger; 5 – intermediate storage capacity of hydrogen and oxygen; 6 – place of the steam-hydrogen overheat; 7 – separator-steam superheater; 8 – plot for filing of the condensate to the system of water electrolysis; 9 – condensate capacity tank for the electrolysis

During the peak load in the power grid, hydrogen and oxygen from storage tanks come in compression to a working pressure of fresh steam at the inlet to the to a head of steam turbine. Electricity for the booster compressors is assumed to consume from the nuclear power plant. Intermediate tank of hydrogen and oxygen can smooth out fluctuations in the supply of gases in a plot steam-hydrogen overheating.

The location of the energy complex with hydrogen fuel can be carried out at a separate area at an acceptable distance about nuclear power plant. This task in this paper is not considered, but will be developed in future.

New feature of the scheme of the hydrogen cycle is to use a booster compressors after the storage tanks. This eliminates the accumulating hydrogen and oxygen at pressures much higher than operating pressure steam of steam turbine (6 MPa in this example).

Effective use of hydrogen fuel in the cycle of nuclear power plants to produce additional (peak) power can be carried out by steam-hydrogen overheating of fresh steam. In this case the steam-hydrogen overheat can be carried out by a two-step oxidation of hydrogen with oxygen [1, 2, 3]. In this case it is possible to eliminate the use of the component cooling. This allows the most efficient use of summing up the heat of hydrogen fuel. It is assumed that high-temperature steam formed in the system cooled by fresh steam and not moving on any connecting pipeline.

The use of steam-hydrogen overheat on the existing turbines is possible only within their power to more nominal. For NPP turbines made to existing projects, the possibility of increasing capacity within a 100 MW.

In place of the steam-hydrogen overheat high-temperature steam is mixed with fresh steam of turbine NPP. This can significantly increase the temperature of the working steam before the steam turbine. It may be necessary to upgrade equipment of steam turbine in the first place, the cylinder pressure, and electrical parts. As a result steam-hydrogen overheating leads to the production of additional peak power. At the same time the work of the reactor and steam generators remain unchanged.

Return of the added part of the working steam of the cycle of the atomic power station as a result of steam-hydrogen overheat in the process of electrolysis, it is advisable in a heated condensate (after a low-pressure heaters). Thus, it will enhance the efficiency of water electrolysis process in its implementation of the pressure [4, 6]. In such a closed loop operating costs at the chemically treated water can be ignored.

Justification Use Electrolysis Increased Power To Produce Hydrogen And Oxygen

Most effectively to carry out the process of electrolysis under pressure [4-8]. For example, we know that it is expedient to increase the system pressure electrolysis from atmospheric to 1 - 5 MPa, and the process temperature is 120 – 160 °C [7].

The current electrolysis plant (Russian or foreign) have low power. Maximum power of currently available electrolyzers is 3 MW. Production in Russia, Chemical Engineering Company in the city of Yekaterinburg. Therefore, for large-scale production of hydrogen and oxygen during the night off-peak power consumption atomic power station they are needed in large quantities (up to a thousand or more). This requires considerable space, numerous attendants, as well as complicating the control of production.

In this connection it is necessary to create electrolysis plant increased power, with the possibility of operating with frequent starts and stops without reducing the service life [1]. Thus, based on [1], the power of the electrolysis plant of energy complex with hydrogen fuel adopted by 50 MW.

Thus, based on [1], the power of the electrolyzers of energy complex with hydrogen fuel adopted by 50 MW.

Justification And Assessment Of Cost Of The Storage Of Hydrogen And Oxygen In A Daily Cycle

Feasibility of a particular method of storing hydrogen in the long run, will be determined by its cost, weight and volume indices, power and performance characteristics (for example, the dynamics of accumulation and output of hydrogen).

A detailed comparative analysis of alternatives for hydrogen storage was carried out by many authors. Among the recommendations regarding the use of common methods of storing hydrogen in a variety of applications, there are underground storage tanks, both natural and man-made, high-pressure composite cylinders, organic hydrides, metal hydrides, cryogenic vessels, both high and low pressure [9].

Production of hydrogen and oxygen in the off-peak nighttime periods of electrical load may require large-scale storage. Specificity of storage of hydrogen and oxygen under these conditions is associated with daily accumulation and output from the storage system.

Underground storage method of large quantities of hydrogen is the most preferred [9, 10]. However, in the daily cycle of the application of underground storage creates certain technical difficulties. When the period of storage of hydrogen and oxygen can be from several hours to several days, is most suitable on the ground (underground) storage in a compressed form in special by metal storage capacity (cylindrical or spherical gas holders) [11, 12].

As the storage system of hydrogen and oxygen in this case are considered on the ground cylindrical storage capacity of 100, 400, 800 m3 with spherical bottoms, in which hydrogen is pressurized [11].

In table. 1 shows the results of calculations of the specific investments in storage capacity of hydrogen and oxygen taking into account production, assembly and automation.

Table 1 – Specific Investment In Storage Capacity Of Hydrogen

And Oxygen Volume Of 100, 400 and 800 m³

Pressure Storage, MPа	Specific Investments In Storage Capacity This Volume, dollar/m^3
	100 m^3	400 m^3	800 m^3
2,2	320	350	350
4,2	650	600	590
6,4	950	910	850

Lowering of the specific investments in capacity with an increase in its volume at a pressure of accumulating 4.2 and 6.4 MPa due to a decrease in the estimated value of the resistance of steel with an increase in its thickness (due to the increasing pressures on the storage capacity walls) [13]. This value, depending on the thickness of steel, has an impact on the cost of production. In the case of accumulation of 2.2 MPa pressure with an increase in capacitance value of the calculated resistance of steel is higher than in versions 4.2 and accumulation of 6,4 MPa. Therefore, specific investments in storage capacity are increase.

The results of calculation of the specific investments in storage capacity of volume of 100, 400, 800 m3 deposited per unit mass of hydrogen and oxygen made from steel 09G2S, in the temperature of storage of hydrogen and oxygen of 7 °C to 27 °C are shown in Fig. 2, 3.

t = 7°C

t = 27°C

a

t = 7°C

t = 27°C

b

t = 27°C

t = 7°C

c

Fig. 2 – The Dependence Of The Specific Capital Investments Per Unit Mass Of Hydrogen Stored In Storage Capacity Of Volume: a – 100 m³, b – 400 m³, c – 800 m³

t = 27°C

t = 7°C

a

t = 27°C

t = 7°C

b

t = 27°C

t = 7°C

c

Fig. 3 – The Dependence Of The Specific Capital Investments Per Unit Mass Of Oxygen Stored In Storage Capacity Of Volume: a – 100 m³, b – 400 m³, c – 800 m³

From these data presented in Fig. 4 and 5 shows that the storage of hydrogen and oxygen more efficiently use a larger storage capacity (400-800 m³) and in the pressure range 4 – 6.5 MPa. In the scheme of the energy complex with hydrogen fuel (Fug.1) a pressure in the storage system is accepted 4 MPa.

This method of storing hydrogen in storage capacity is competitive in terms of specific power inputs and value indicators in comparison with other methods (Fig.4, 5).

Fig.4 – Competitive Energy Costs For The Implementation Of Ways To Store Hydrogen In By Metal Storage Capacity

Fig.5 – Competitive Cost Performance Of Hydrogen Storage In By Metal Storage Capacity

For example, at a pressure of 4 MPa and the storage temperature of 27 °C range of specific investment in storage capacity with the increase of its volume from 100 to 800 m³ of 205 – 185 dollar/kg H₂ or 6.0 – 5.5 dollar/kWh, respectively. From a comparison shows that the storage of hydrogen in a compressed form in storage capacity of cylindrical type is competitive with the way the use of chemical hydrides. At the same time, such methods of storing hydrogen as a metal hydride, cryogenic and compressed in cylinders under high pressure are uncompetitive.

Evaluation Of Technical And Economic Parameters Of The Energy Complex With Hydrogen Fuel

Table 2 presents some technical and economic parameters of the energy complex with hydrogen fuel at nuclear power plant.

Table 2 – Some Technical And Economic Parameters Of The Energy Complex With Hydrogen Fuel

	Use power for the production of hydrogen and oxygen (МW) / temperature of overheated steam at the turbine inlet (°С)
	100 / 290	500 / 376	1000 / 503
Investment in energy complex with hydrogen fuel, thousand dollars/kW (peak power)	0,3	0,93	0,89
The volume (mass) production of hydrogen, thousand normal m^3/day (thousand kg/day)	126,5 (11,4)	632,5 (57,0)	1270 (114)
The volume (mass) production of oxygen, thousand normal m^3/day (thousand kg/day)	63,24 (90)	316 (460)	635 (900)
Peak power (electric power) АЭС, kW (kWh/day)	54500 (272400)	301000 (1505000)	610800 (3054000)
Effective use of hydrogen fuel in the cycle NPP , %	71,8	80,0	80,6
The efficiency of the use of off-peak electricity NPP , %	38,9	43,5	43,6
Efficiency of NPP gross/net, %	34,18/32,37	37,37/35,53	40,62/38,71

Thus, by using steam-hydrogen overheat increase the efficiency of power block of atomic power station may amount to gross 0.9-7.3%, and 0.7-7.0% net.

Competitive Efficiency Of Energy Complex With Hydrogen Fuel And The Pumped Storage Plant

Comparison of atomic power station with energy complex with hydrogen fuel and the pumped storage plant to production of peak electricity (capacity) was carried out with the equal consumption of the off-peak electricity of the night time. Night off-peak period electrical load is assumed to be equal 7 h/day number of hours of use energy complex with hydrogen fuel and the pumped storage plant for the production of peak power (capacity) is assumed to be equal to 5 h/day. Number of hours of use for a NPP power unit in the year is assumed to be equal to 7000 h / year. The tariff for peak electricity is assumed to be equal. Comparisons carried out to the depending on proportion used by off-peak power NPP power unit. Horizon calculation is assumed to be equal 25 years, discount rate constant on the horizon and equal to 0.1. Were taken into account methodical recommendations on evaluation of investment projects. The options were reduced to equal the energy effect [2].

The advantage of the energy complex with hydrogen fuel is the ability of its location near the atomic power station with the consumption of electricity at the its self cost. It is virtually impossible in the case use of pumped storage plant. In this case, pumped storage plant consumes electricity from the grid on tariff that exceeds the cost of electricity in two to three times. In addition, the location of the energy complex with hydrogen fuel near the atomic power station reduces the electricity losses during transmission.

In Fig. 8 is shown net discounting profit, depending on the use of off-peak power of NPP power unit, and various ratios of the tariff for consumption of electricity from grid and from atomic power station: ξ = 1, 2, 3.

Fig. 8 – Net Discounting Profit Of Energy Complex With Hydrogen Fuel And Pumped Storage Plant: 1 – energy complex with hydrogen fuel; 2-4 – pumped storage plant (k = 1000 dollars/kWh, ξ = 1, 2, 3); 5-7 – pumped storage plant (k = 1500 dollars/kWh, ξ = 1, 2, 3)

The most effective option is the pumped storage plant with specific investments not exceeding 1000 dollars/kW. Consumption of electricity from atomic power station at self cost (ξ = 1, line 2). But using off-peak power of 100 MW is more efficient variant of the energy complex with hydrogen fuel.

Variants for using pumped storage plant with k = 1000 dollars/kW, ξ = 2 and for k = 1500 dollars/kW, ξ = 1 are competitive with energy complex with hydrogen fuel (lines 3 and 5, respectively).

Variants for using pumped storage plant with k = 1000 dollars/kW, ξ = 3 (line 4) and for k = 1500 dollars/kW, ξ > 1 (line 6 and 7) are uncompetitive with energy complex with hydrogen fuel.

The index income and payback period of the energy complex with hydrogen fuel is estimated:

– when using off-peak power 100 MW of NPP power unit: index income 2,6 dollar/dollar, payback period ≈ 9 year;

– when using off-peak power 500, 800, 1000 MW of NPP power unit: index income 2 dollar/dollar, payback period ≈ 12-13 years.

Conclusion

The set of technical challenges and risks in the construction of pumped storage suggests their location is not near a atomic power station. This leads to the consumption of electricity during the night time at tarrif of electricity greater than the self-cost electricity of atomic power station in more than 2 - 3 times. This significantly increases the competitiveness of hydrogen cycle on atomic power station even at a more lower efficiency of production of electricity in peak times.

The most effective option is the pumped storage plant with specific investments not exceeding 1000 dollars/kW. Consumption of electricity from atomic power station at self cost. But using off-peak power of 100 MW is more efficient variant of the energy complex with hydrogen fuel.

Competitiveness of the pumped storage plant is markedly reduced when specific investments over $ 1,000 / kW and the tariff of electricity is 2-3 times higher than the self cost of electricity of atomic power station.

These results indicate the presence of zones of competitive efficiency of atomic power station with energy complex with hydrogen fuel at compare with pumped storage plant.

These developments allow to take into account the specific conditions of construction of power plants with the accumulation of electricity at comparing their efficiency.

Sources Used

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