MGA THERMAL STORAGE IMPLEMENTATIONS
Assembly Into Storage Blocks
Manufactured MGA units are modular and can be assembled into large storage blocks with integrated heat transfer tubing. This concept is illustrated below. Such blocks are suitable for any large scale thermal storage application including direct-steam production from any heat source for steam turbine driven electricity generation.
Concentrated Solar Tower Thermal Power Plant
In concentrated solar power tower plants, the sunlight is focussed onto a receiver which then either stores heat directly or transfers heat, via a transfer fluid, to a storage facility on the ground. Due to their excellent thermal conductivity, MGA are excellent candidates for a directly irradiated thermal storage module. The stored heat is then available to generate high temperature – high pressure steam for use in conventional Rankine cycle turbine-generators the same as used in fossil fuel power stations.
Graphite has been demonstrated to be an effective low-medium energy density storage/receiver. A similar concept can be used for Miscibility Gap Alloy thermal storage in which the storage block also acts as the steam boiler. As MGA can store up to ten times as much heat as graphite (per unit volume), they are purpose made for this application. Due to mass considerations, redirecting the focused sunlight towards a Miscibility Gap Alloy thermal storage block located on the ground may be economically advantageous.
Graphite has been demonstrated to be an effective low-medium energy density storage/receiver. A similar concept can be used for Miscibility Gap Alloy thermal storage in which the storage block also acts as the steam boiler. As MGA can store up to ten times as much heat as graphite (per unit volume), they are purpose made for this application. Due to mass considerations, redirecting the focused sunlight towards a Miscibility Gap Alloy thermal storage block located on the ground may be economically advantageous.
Conventional Thermal Power Plant
Thermal inertia is very useful in conventional power generation. Large steam turbines used in coal, gas and nuclear power plants take a very long time to reach operating speeds. Interruptions to the supply of steam causing a turbine to be taken offline, interrupt power generation at significant cost. Interruptions that stem from heating/pressurizing the steam may be minimized through a thermal storage medium such as MGA.
Modern thermal power stations operate with super critical steam at high pressure (>22.1MPa) and temperature (>650°C). Miscibility Gap Alloys can be heated through the burning of fuels to very high temperatures. Unlike competing storage systems, there are MGA that can store and deliver heat at these high temperatures. Their high thermal conductivity would allow an MGA storage/boiler to be constructed.
Introducing storage to a thermal power plant would allow for the switching of fuels whilst still maintaining steady power generation. A plant that utilized a combination of biomass, waste burning and coal for example, could change burning temperature and heat transfer rates with minimal impact on the power cycle operation in the short term. A greater period would be available where the boiler need not be fired as preparations were made for the next fuel source.
Modern thermal power stations operate with super critical steam at high pressure (>22.1MPa) and temperature (>650°C). Miscibility Gap Alloys can be heated through the burning of fuels to very high temperatures. Unlike competing storage systems, there are MGA that can store and deliver heat at these high temperatures. Their high thermal conductivity would allow an MGA storage/boiler to be constructed.
Introducing storage to a thermal power plant would allow for the switching of fuels whilst still maintaining steady power generation. A plant that utilized a combination of biomass, waste burning and coal for example, could change burning temperature and heat transfer rates with minimal impact on the power cycle operation in the short term. A greater period would be available where the boiler need not be fired as preparations were made for the next fuel source.
Trough Concentrator Solar Thermal Power Plant
Concentrated Solar Troughs provide a means of focusing sunlight upon either a heat transfer fluid or directly on a working fluid. The fluid can then heat the thermal storage material or travel directly to the turbine. This arrangement is shown schematically in the figure below.
In addition to the thermal storage block concept illustrated above, an adaptable and low cost method of using Miscibility Gap Alloys for thermal storage was developed by Dr. Anthony Rawson (PhD thesis, University of Newcastle, 2016). The thermal storage device utilizes 200L (44 Gallon) steel or stainless steel drums as the outer encapsulation for a Miscibility Gap Alloy. Drums were chosen
as they are a convenient volume and extensive infrastructure exists in transport and manufacture. As shown in the figures, a central pipe carries the working fluid through each barrel and acts as the heat exchange
surface. Barrels are placed on their side and arranged in an array of series and parallel blocks to achieve the required storage and discharge requirements of the particular power cycle (a possible configuration is demonstrated in the figure). The barrels may be placed in a shipping container which might be flooded with an inert gas if required.
High conductivity Miscibility Gap Alloys are particularly well suited to the single pipe design. Low conductivity materials like salts and concrete would require additional heat transfer area to effectively take advantage of a barrel storage system.
Air Heating
The device is illustrated in below. It consists of an insulated shell in which blocks of Zn-C Miscibility Gap Alloy could be stacked to achieve the dimensions of 600 x 600 x 200mm (72L). The blocks are stacked within a caddy that can be easily inserted and removed. The shell is ducted to a fan with variable speed control and a set of backdraft shutters. Around the caddy are four shutters that can be manipulated by hand to adjust the air flow path over the surface of the blocks.
Other Implementations
Many industrial processes benefit from thermal inertia whether taking advantage of a steady heat transfer or in consuming off peak or intermittent power sources. Steam generation, drying and cement production are three examples where Miscibility Gap Alloys could improve the cost and efficiency of the process.
Steam Generation is important in many industrial processes. Fuel and power usage can be shifted to lower cost periods by boiling water using a heater incorporating thermal inertia (storage). Depending on the steam requirements, the appropriate Miscibility Gap Alloy would change (see “Advantages of MGA” page). For low grade steam used in cleaning Pb-Sn-Al or Zn-C would be appropriate. For steam to be utilised in power generation or chemical reactions Mg-Fe, Cu-Fe or Cu-C might be better suited.
Drying of food, timber products or waste products is common in industry. A thermal storage system can be used to utilise renewable energy such as sunlight and yet to continue operations throughout the night. Zinc-Graphite has a convenient operation temperature (420° Celsius) for heating air. Forced or natural convection over or through an encapsulated block of Zn-C would provide a useful stream of hot air for drying processes.
High temperature industries can readily benefit from thermal storage. Silicon-Silicon Carbide MGA (1411°C operating temperature) operates at a useful temperature for calcinating and/or fusion processes. In clinker production for cement manufacture temperatures of ~1500°C are used whereas glass production needs furnace temperatures of ~ 1600°C. Given cement and glass manufacture are extremely energy intensive, MGA thermal storage has the potential to maintain high furnace temperature for continuous production whilst paying only off-peak rates for electricity or gas or even using solar PV or concentrated thermal power to provide energy through the day to the storage material.
Large ocean going vessels would benefit significantly from increased range. Only a fraction of the chemical energy available in the combusted fuel is converted to thrust for the ship. An additional power cycle to take advantage of the high temperature exhaust gases expelled after combustion could be utilised. These exhaust gases vary in flow rate and temperature depending on the requirements of the ship. Thermal storage utilising Miscibility Gap Alloys can capture the heat from the exhaust and transfer it to the secondary power cycle thus providing storage and effective heat transfer.
A huge variety of applications exist for Miscibility Gap Alloys. Due to their variable operating temperatures, durability, energy density, thermal conductivity and safety the materials are extremely competitive with existing methods. Their unique properties also open up new fields of application that have not had appropriate thermal storage solutions until now.
Do you have any citations or sources?
ReplyDelete