A Novel Pumped Hydro Combined With Compressed Air

7/28/2019 A Novel Pumped Hydro Combined With Compressed Air

1/45

Garma Russell

Mndez Adn

Mitz Enrique

Uc Andrs

A Novel Pumped Hydro Combined withCompressed Air Energy Storage

System


2/45

Abstract

A novel pumped hydro combined with compressed

air energy storage (PHCA) system is proposed in

this paper to resolve the problems of bulk energy

storage in the wind power generation industry

over an area in China, which is characterized by

drought and water shortages.

This paper discovers how some parameters affect

the performance of the whole system.


3/45

Introduction


4/45

Introduction

Using storage technologies combined with green

power sources is one of the methods for reducing

the negative effects of these resources on power

systems [1].

However, there are still problems in the modern

industry for such large-scale energy storage

systems.

In China, the wind power industry has been

developing rapidly in the past 20 years, and large

scale energy storage has become very

prominent.


5/45

Introduction

As wind energy fluctuates, randomness causes

the existing national grid to be unstable if wind

power joins the national grid.

The current paper proposes a novel methodology

for a large-scale energy storage system in a

drought-prone area


6/45


7/45

Comparison ESS

There are only two kinds of mature technology suitable for

wind power storage: pumped hydro energy storage

(PHES) and compressed air energy storage (CAES).


8/45

Background

Grazzini et al. [11] proposed the concept ofAdvanced Adiabatic Compressed Air Energy

Storage (AA-CAES).

Kim et al. [12] proposed a water-compensated

CAES system, which utilizes a water head

supplied by an aboveground reservoir to keep the

storage cavern at a constant pressure throughout

operation.

The two novel systems can save energy, but their

structures are complicated and existing CAES

systems require extra power to increase the air

temperature, thus leading to high energy storage

costs


9/45

PHES - CAES PHES has been constrained by market

uncertainties, localization difficulties, andenvironmental impacts [4]. Consequently, PHEScannot be used to store the vast majority of wind

power in China. CAES is a promising energy storage method, with

high reliability, high economic feasibility, and lowenvironmental impact [5,6].

The current paper proposes a new energystorage system, which combines the advantagesof the PHES and CAES system. The novelsystem is called pumped hydro combined withcompressed air energy storage (PHCA).


10/45

Physical Model and Working

Principles


11/45


Principles

A PHES facility is typically equipped withreversible pumps or generators connecting an

upper and a lower reservoir. During off-peak

hours, the pumps utilize relatively cheap

electricity from the grid to move water from thelower reservoir to the upper one in order to store

energy. Meanwhile, during periods of high

electricity demand (peak-hours), water is released

from the upper reservoir to generate power at ahigher cost [13].

How is this technology to be employed in a

drought or plain area?


12/45


Principles

A pump is connected to an air container trough a valve,and when water is pumped to the vessel, the pressure

of the air increases as the volume is fixed. This is

equivalent to raising the water level.


13/45

Operation Process

Initially closed valves include valves 6, 7, 9 and 10. The

valve open is 8 and starts the compressor 4, pumps the

air to the vessel, thereby setting up a pre-set pressure in

vessel 5. Compressor 4 and valve 8 are closed when thepre-set pressure has built up.


14/45

Operation Process

For storing energy, we open valves 7 and 9, and inject

water to vessel 5 by starting the high pressure pump 2.

The pressure in the vessel goes up when the water

surface rises. The air temperature of the compressed air

will increase. At the same time, a small amount of water


15/45

Operation Process

For the generation process, valves 6 and 10 are opened.At this point, high pressure water pushes hydro turbine,

which powers the generator, generating electricity.

Meanwhile, a small amount of water flowing through valve

10 is sprayed to the expanded air and exchanges heatwith the air.


16/45

Characteristic of the PHCA System


17/45

Quality Energy

The quality of mechanical energy is better than

the thermal energy [14].

In the PHCA, energy is converted from

mechanical energy (pressure energy) to electrical

energy through the turbine.

The thermal machinery (compression/ expansion)

of the CAES is substituted by hydraulicmachinery (pump/hydro turbine) of the PHCA


18/45

Thermal and hydraulic machinery

Example:

In order to obtain a shaft power of 60,000 kW, the

working medium in the turbine needs to get

through sixty stages continuously with an initial

pressure of 25 MPa.

While for the hydro turbine, the same power can

be obtained after the working medium goes

through one stage of energy conversion with an

initial pressure of 1~3Mpa.

The structure of hydraulic machinery is more

simple than the thermal machinery.


19/45

Costs CAES vs PHES vs PHCA

The main equipment cost of 1MW energy storage is

investigated and the total cost thus inferred (including

electrical and controls, construction materials, labor, indirect

costs and so forth) according to [15,16].


20/45

Costs CAES vs PHES vs PHCA

Low cost. In the same scale of energy storage system, the

costs of high pressure water pump and hydro turbine are

less than those of the compressor and expander,

furthermore, the PHCA does not need a cooler or heater.


21/45

Comparison PHCA vs

CAES/PHES Simple structure. In the process of energy

storage and power generation of the PHCA,cooler and auxiliary heating systems are notrequired.

High efficiency. The efficiency of the water pumpand water turbine are both higher than that of thecompressor and expander, thus, the efficiency ofthe PHCA has a more improved space than theCAES.

Compared with the structure of PHES [14], thePHCA does not need special geologic conditions.It has the advantages of little water supply andevaporation problems, and water energy storage

density can be easily changed.


22/45

1. Initial Compression Process

2. Water injection Process for Energy

Storage

3. Electricity Generation

Thermodynamic Analysis of the

PHCA System


23/45

Simplifications and Assumptions Nitrogen:

Very low solubility in water

Inactive and easily accessible

Treated as ideal gas

Water incompressible Vessel adiabatic container

No net transfer or water vapor between the water andnitrogen

No pressure loss in the pipes

The compressor is working under a non-steadyprocess.

The real compression process can be treated as anoverlap of many tiny steady compression processes


24/45

Initial Compression Process

Adiabatic compression process, work per unit

mass of the gas injection is calculated as follows:

(1)

P0: Initial pressure of the vessel

P: Pre-set pressure of the vessel


25/45

Initial Compression Process

Assuming the total volume Vh then according tothe ideal gas equation:

(2)

The total mass is injected as follows:

(3)


26/45

Energy consumption

The total energy consumption can be presentedas:

(4)


27/45

Water Injection Process for Energy

Storage

The high pressure water pump injects water into water-airmix up vessel. As the water level raises, the nitrogen in the

vessel is compressed. At the same time, the water flowing

through valve 9 is sprayed onto the compressed air so as to

decrease the air temperature.


28/45

Water Injection Process for Energy

Storage

After water feeding and before heat exchange,the gas temperature is as follows:

(6)

Where is the volume ratio of water to air:

(7)

After heat exchange water and nitrogen becomes

(8)


29/45

Water temperature

Combining equations (5-8), Tw could be resolvedby the following formula:

(9)

Where:

(10)


30/45

Tw -


31/45

Tw P1


32/45


33/45

After the isothermal water charging, nitrogen

pressure is P2, then water volume is given by:

(11)

If the height differences between the pond and

the vessel is negligible then pump work per unit

mass would be:(12)

Total pumped energy consumption:

(13)


34/45

Electricity Generation

If all energy losses are neglected, water pump

energy consumption should be equal to the work

produced by the water turbine energy:

(14)


35/45


36/45

Analysis and Discussion of

Influencing Parameters

The pressure vessel is one of the most important

facilities in the PHCA, because its capacity affects

the cost of system.

The total work input and output per cubic meter

must be identified in order to optimize the system:


37/45

The influence of Work Density

Then, the work density is defined:

Pump and water turbine work density varies

against pre-set pressure, and water-air volume

ratio.


38/45

Work density graphics

Both items increase when pre-set pressure and water-air

volume ratio is increasing.

Ch R l ti P V


39/45

Change Relations among P1, Vh,

Ch R l ti P V


40/45


Change Relations among P V


41/45



42/45

Graphics Conclusions

It is found that any two or the pre-set pressure,

vessel volume and water-air ratio have an inverse

relationship, such that as one parameter

increases, the other decreases. In addition, whenone parameter increases to the allowed maximum

value, the other decreases slowly.

I fl f W P Effi i


43/45

Influence of Water Pump Efficiency

and Water Turbine Efficiency

In the work process of the PHCA, the compressor

just works for initial pressure, the system

efficiency are:


44/45

Conclusions

1. The PHCA has advantages:1. Simple structure

2. High efficiency

3. Low cost

- Compared with the CAES

- Not special geologic conditions (like PHES)

2. On the premise of assuming the charge and

discharge as an isothermal process, the PHCA

efficiency is proportional to the pump efficiency

and water turbine efficiency.


45/45

Conclusions

3. The work density is increasing when pre-setpressure and water-air ratio are increasing. And

any two of pre-set pressure, vessel volume and

water-air ratio have an inverse relationship in the

condition of certain total work input and output.- This result can play a guiding role in constructing

a specific power system.

Documents

A Novel Pumped Hydro Combined With Compressed Air