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POLYGENERATION
 
 
When power is generated, more than half the energy is in the form of heat. Most of the heat is dissipated and lost. The economics of power generation then become dependent entirely on the cost of producing the electricity. Despite the low level of energy being used for electricity, using diesel in generators is still one of the cheapest ways of producing electricity. But this diesel electricity ratio varies greatly by location. We are not all in the enviable situation of those who are in oil rich countries with local prices lower than world market rates. When delivered in small quantities to remote locations, diesel becomes far more expensive.

Co-generation recovers heat energy and the value of the system depends on the commercial value of the use to which the heat is put. Polygeneration tries to maximise use of that heat value. In transforming heat value to money a great deal depends on the efficiency and extent to which the heat can be used and the value of the benefits gained. It is rarely possible to use all the heat generated. If there were ways of using that heat for viable commercial purposes, the discussion on polygeneration systems would revolve on maximising revenues and physical efficiency. 

Biogas, Biomass Solar, wind are all familiar sources of renewable energy. However, they are all more expensive sources than current fossil fuels. The cost of electricity is, of course, crucial in determining the viability of most commercial enterprises. At present, in the most advanced countries, the most efficient enterprises may try to achieve US 6 cents per kWh. The current commodity price for electricity is around 8-10 cents.
 
Enterprises in developed countries have the above energy cost benchmarks to guide them. If renewable energy cost more, they are often subsidised. In developing countries the figures are distorted sometimes by levies and taxes as is the case in Kenya which increase utility rates above benchmark. However, more remote areas and countries such as small island states in the Pacific have a freight problem in transporting diesel or coal in small quantities for long distances. Moreover, they have Utility companies which do not face any significant competition. So, it is not unusual to end up paying 20 cents per kWh and not unknown to pay 40 cents. At these prices, all business activity that has energy as an important cost component becomes far less likely to be viable. Fuel for vehicles is also far more expensive than in developed countries.
 
In such situations, the renewables that are still far more costly than benchmark fossil sources, become viable albeit at a range of prices above global benchmark energy rates. Solar, tidal and wind power also require substantial capital costs that agricultural communities in least developed countries and remote ones can afford. However, many of the latter have biowaste that can be used as source for gas or fuel.
 
Larger developing countries often have electricity grids that do not cover remote areas. Loses during transmission and leakages add to the high capital costs involved. Over one-third the world's population has no access to electricity. They do have animal waste and agricultural waste as do the smaller remote countries. However, a system based on transforming agri-waste into energy is at best marginally viable and often not viable at all.
 
Polygeneration is a system being developed by technically advanced companies like HVR AB in Sweden and it is based on the idea that if you can derive multiple end-uses and thus revenue flows from biogas and bio-mass solutions, the systems are more likely to be viable. Vinay Chand is actively involved in these efforts and is, in fact Chairman of HVR. The objective is to develop optimal solutions that can be purchased, delivered and operated in a simple manner. HVR is working in close collaboration with KTH (The Royal Institute of Technology in Stockholm) to develop and test concepts and then to test them in physical form.
 
Two applications have been developed and tested:
 
1       BANGLADESH
 
In Bangladesh there is a often poor rural access to electricity, cooking fuel, drinkable water (with arsenic poisoning ruling out much of the well water) and heat for crop drying. They do have a great deal of animal waste from dairy and poultry farming. The idea is to use cow dung to generate producer gas for cooking, as fuel for electricity, to distil arsenic contaminated water and provide heat for crop drying. In addition the slurry that remains can be sold as fertiliser.
 
Five revenue streams render small village based decentralised systems economically viable. SIDA, the Swedish Development Agency financed three years of research and development, implemented by the Royal Institute of Technology (KTH), HVR and Grameen Shakti which has led to the translation of the concept into physical reality.
 
 
The five revenues would each add to the profits earned by the small system devised. Water and electricity revenues are the most important.
 
 
 

2     SMALL ISLAND PAICIFIC STATES
 
Thousands of islands in the Pacific are covered in coconuts but most have poor or no access to electricity or drinkable water and face very high electricity tariffs and high diesel prices. When oil or diesel is transported to some of the smaller islands, it is in barrels which raises freight rates to an alarming extent. However, nearly all tropical islands do have coconuts even though they may not be able to make much commercial use of them.

By using coconut shells as the source for gas or mass, it is possible to generate electricity, distil water, dry crops and recover the residue as barbecue charcoal or use it for production of activated carbon. Each remote island can become self sufficient in energy, drinking water and electricity and yet make a profit based on using the abundant supply of coconut shells. Moreover, some of the waste heat could be used to dry copra which could then be expelled for oil to be used as fuel for boats.

In Vanuatu on Santo there is a village (Port Blair) based system that uses coconut oil as fuel to supply electricity to the entire village. The system has now been functioning for over 10 years and is viable. In this case, entire coconuts were considered to be surplus to requirement for human consumption.

Revenues from charcoal alone are sufficient to commercially justify the system. Therefore, pricing in the different revenue flows becomes more flexible. Coconuts are a renewable sustainable, eco-friendly source of much of what these small islands need for their survival. There are usually more coconuts than can be consumed by small populations and production of copra or oil for export would not be competitive in global markets. In Samoa, for example, coconuts are even fed to the pigs and that is not uncommon. 

We bring together the experience of Vinay Chand in the coconut sector globally and, in relation to this, in the Pacific Region. He has been looking at development possibilities in: the Cook Islands; Fiji; Kiribati; Papua New Guinea; Samoa; Solomon Islands; Tonga; and Vanuatu. The development potential of coconuts was the most important crop looked at. And combine it with work by Scarab, Xzero and HVR in water purification based on waste heat. Scarab AB is the source of the water technology and was the originator of the Integrated Coconut processing concept.
 
HVR has designed a prototype that produces 25kWh of electricity, dries copra and cocoa and distils water ion a module that should fit a 20 foot standard container. We estimate it to be very profitable.
 
coconut shells
 

Systems and Components of the Plant for coconut shell based biogas polygeneration

 

The following systems and components are provided to accomplish the above functions:

 

- Bark conveying, screening/sizing and delivery

- Coconut shell drying system

- Gasification process air supply

- Down draft gasifier system

- Product gas cooling and cleaning system

- Gas feeding to biogas engine with external heat exchangers for exhaust gas heat recovery (Two or three HX)

- Ash removal

- Membrane distillation (MD) unit

- Feed water tank for MD water purification unit

- Two pumps for cooling and feed side of MD

- Cooling water supply to MD

- Piping, valves, temperature and pressure indicators etc.

- Control system

- Electricity and water distribution system

 

 

Polygeneration Economic parameters (approximately estimated values)

Particulars

Unit

Coconut shell gasifier 

System capacity

kWe

25

Life  of  gasifier—engine system

Year

12-15

Life  of  distribution network

Year

12-15

Distribution line network (average)

km

3

Auxiliary consumption and technical loss

%

10

Membrane distillation (MD) unit

Year

20

 

 

 

Digester

USD

   10,000

Gas engine

USD

40,000

MD unit and auxiliaries costs

USD

45,000

Civil  Shed

USD

  7,000

Control system

USD

  8,000

Crop drying shed

USD

  5,000

Cost of  PDN  (3 km)

USD

  5,000

Total Cost of System

USD

120,000

 

Table 2: Coconut shell Characteristics
Biomass  C(dry wt%)HNSOClAshHHV (MJ/kg)
Coconut shell46.67-48.85.43-5.70.55044.030.732.5818.56-22 MJ/kg

 

 Charcoal alone would be able to cover costs of the proposed system with a healthy bottom line. Polygeneration system economics are greatly strengthened when there is an end product in addition to electricity, heat and gas to sell.

 

annual US$
Capital cost depreciation                   12,000
Labour                   12,500
Shells                     3,000
Maintenance                     6,000
Total cost                   33,500
Electricity kWh                   12,600
Water litres                   10,080
Charcoal                   60,000
Crop drying                   15,000
Revenue                   97,680


The possibility of developing village scaled systems that are easy to buy, deliver and operate would allow villages to own their own systems and, as such, to decide on relative charges and prices. It would be possible to make either electricity or water free. Moreover, the system could be owned and operated on a non cash basis. Purchase of coconut shells and sales of electricity, water and crop drying, could all be made book transfers.

 

The polygeneration system using coconut shells has been included in the Regional coconut Development proposal awaiting finalisation of funding from the EU and is also of interest to private buyers in the form of co-operatives and processing plants. The coconut oil mill in Santo, Vanuatu, is already using some of the coconut oil they produce for energy. A plant at Port Orly, Santo, Vanuatu has for over 8 years now been operating a system where fresh coconut meat is pressed for oil that is filtered and then used to generate electricity for the second largest urban concentration on the island. Consumers have electricity delivered to their homes and can access it using pre paid smart cards. The system was financed as a pilot by the EU and is a good success story. We have visited it personally and can attest to that fact. Of course, these two are examples of co-generation rather than polygeneration but are a step in the right direction.

 

Sida, the Swedish Aid Agency, we are told intends to finance some pilot plants to promote environmentally friendly innovative developments and this is a very good and long overdue decision. It is much better than Technical assistance in the form of telling people what the solution is when they really need pilot plants to move to the next phase. We wait eagerly for Sida to act.


The MD module

Xzero AB

 

www.hvr.se

www.xzero.se

 

HVR is promoting Polygeneration particularly when based on bio-waste but use modules made by Xzero who are upscaling systems for use as rinse water stations for the semiconductor industry. A number of 500 litres per day capacity MD units have been used for testing and there is a 5,000 litres per day unit being tested near Stockholm where there is particular pollution from the pharmaceutical industry.

HVR has also been undertaking development work in UAE on solar powered polygeneration with solar panels used instead of coconut shells. It all depends on the availability of coconut shells and the relative costs involved which we will be calculating before the end of November 2015.

Demonstrations are intended for Bangladesh and for the Pacific Region.
 
 
 
 A larger scale purification system like the one above for testing purposes that can clean up textile waste water will be supplied by Xzero AB whose main business is developing rinse water systems for the semiconductor industry. The latter systems also have to be cost efficient and so work best using waste heat.

There are many ways of treating washing and dyeing plant pollution, but ETP systems add to the costs and few clothing manufacturers have much leeway in their revenues. However a polygeneration system incorporating MD reduces costs and can even yield profits. Cleaning up clothing plant pollution can be undertaken at zero cost. The prospect of doing so should excite the development agencies as much as it does us.