Fuel types

1. Biomass - straw
   • Energetic aid consumption of straw
   • Straw handling
   • Straw baling
   • Straw storing, moving
   • Market of the straw, its cost price
2. Biomass - pellet
3. Wood fuelling

Straw fuelling technologies
 - Application opportunities of straw and biomass boilers
 - Periodically fuelling straw bale boilers
 - Automatic straw bale fuelling boilers
 - Combustion regulation - one of the most important part of efficiency
 - Smokegas cleaning
 - Chimney

Suggestion for installation

Fuel types

1. Biomass - straw

   • Energetic aid consumption of straw

   • Straw handling

   • Straw baling

   • Straw storing, moving

   • Market of the straw, its cost price

2. Biomass - pellet

3. Wood fuelling

Straw fuelling technologies

• Application opportunities of straw and biomass boilers
• Periodically fuelling straw bale boilers
• Automatic straw bale fuelling boilers
• Combustion regulation - one of the most important part of efficiency
• Smoke gas cleaning
• Chimney
    
  

Suggestion for installation  

 

Biomass – STRAW

The straw is such an agricultural byproduct, which arises by the production of industrial crops, and which does not have the same features depending on its diversity, when it returns back to the nature, or destructs.

The “straw” which can be used as fuel includes also raps (it can be used as supplementary fuel) and the straw of other seed-producing plants, and in a wider sense, even the corn-stalk bales can be listed here.

The below table shows the approximate annual volume, and – in terms of combustion – the most important parameters of grain straw and corn-stalk on the Hungarian agricultural market. (Unfortunately there is not any exact information given related to the volume of raps straw by the article writer).

Byproduct	Straw (baled)	Corn-stalk
Produced quantity (106/t/year)	4,5-7,5	10,0-13,0
Volume available for fuelling (106/t/year)	1,5-2,0	3,0-4,0
Moisture content by harvesting (%)	10-20	40-65
Moisture content after storing (%)	13-15	22-43
Calorific value MJ/kg (18% moisture content)	13,5	13,0

 
According to some studies the total byproducts volume is annually 24-25 million tons from the 45-46 million tons of agricultural biomass. From this quantity, 13-15 million tons of biomass remains on the fields after industrial and feeding utilization, which means a significant reserve in the country’s energy-balance.

Based on our estimations the volume of biomass – available for fuelling – is annually between 6 and 9 million tons (in our case this biomass “can be understood as straw”, and can be burnt quite effective). However it also must be taken into consideration, that this straw volume is generated all over Hungary quite uniformly, so because of transportation volume and costs, mainly the local, and geographically around the country well distributed, smaller burning appliances are reasonable to install in economic, environment protection and sustainability terms.

 
- The energetic utilization of straw from the potentially free biomass is quite little today – though the country uses its rapidly growing ratio for energy production.

However, a number of economic and environmental protection arguments are beside this type of utilization:

• the giant volume of biomass is natural raw material, and it can significantly decrease the country’s energy dependency,

• the sales of it can contribute to the income increase of the low-income agricultural plants,

• the huge savings on heating energy appears the most even in this field of economy (by the heating cost savings of animal breeding plants, greenhouses and foil houses, crop dryers,  food industrial plants), which  improves the economy further of the agricultural food industrial production,

• based on existing domestic and Danish references – who are world-leader in the energetic utilization of straw – 65-80% savings can be realized on heating invoices (based on real heating invoices) compared to  the gas heating. (It can be even 10 million HUF savings, e.g. in the life of a bigger pig-plant),

• it is very important to know, that the grain straws are quasi  CO₂-neutral, so that they do not really contribute to the increase of the atmosphere’s CO2 content, neither the greenhouse effect,

• the remaining small amount of ash itself is a good quality soil replacer, and this is its general aim of utilization (e.g.: mixing it with liquid manure).

 

- Straw handling, storing, cost price, types of firing

Using the straw as fuel charges some technology decisions to the farmer, who is thinking on having this kind of investments:

 
- Straw handling:

• The straw is suggested to be left outside on the stubble-field, let it become wet a couple of times, because the straw washed out by rain includes less corrosive materials – chlorine and potassium.

• This so called „grey” straw is more efficient to be combusted in the boiler, as the boilers’ life-time lengthens significantly, because some part of the materials which corrode the walls and pipes are not any more in the straw.

• It is worth to take this technology element into consideration in the time of baling, giving orders, or by own technology prescriptions.

 
- Baling the straw:

• The modern straw firing boilers are able to accept the standard small and big size bales purchased from international and domestic trading.

• Together with this it is always suggested to consult the optimal bale size with the boiler’s producer by making boiler-investment decisions, and entering into fuel or baling machine purchase contracts.

- Storing, moving the straw

• The firing efficiency is very important related to the straw storing technology because of the water content and the optimal handling of the bales, and it is also important in terms of energy saving level, so it is not worth to understate it.

• The Hungarian planning and investing habits prefer the covered storages, but this is generally not reasonable, if there is enough free space for the storing, and the investors use the special straw cover which lets the ventilation through, but does not take the water in. These special products can be purchased at some Hungarian boiler producers, distributors as supplementary products.

• The planner should keep the Hungarian fire safety prescriptions by storing.

• The volume and the water content shall be controlled by taking over the straw.

• Moving the straw bales inside the plant does generally not require a separate investment, or staff. The whole, big, round and cubic bales are usually moved by a front loader, or loading tractor, the small bales are moved manually.

• By not whole bale fuelling technologies – which is usually reasonable at greater automation level – special storing, handling, splitting technologies can be considered, which are offered by those boilers’ producers.

- Market and cost price of the straw

• We cannot talk about a unified straw market in Hungary yet, but the rules are expected to come into being soon because of the growth of demand.

• By economic calculations it is worth to ask price quotation from straw suppliers within a distance of 50-100km from the investment place, and take these as basic.

• For a rapid calculation we do not make a big failure, if we count with an average price of 12 Ft + VAT/kg, and we take the 60-70% of this as cost price in case of own production.

• Because of the undeveloped market it is worth to supply the fuel by the suppliers in time, under strict contracts.

2. Pellet

Pellet making means the process of compressing agricultural and forestry materials. Pellet is the round cell compressed 3-25 mm biomass, made by roller compressor. The more compressed, 10-25 mm pellet is called fire-pellet. The bio-pellet available for fuelling aims or fire-pellet’s main feature is the great density (1-1,3 g/cm3).

The bio-pellet is made from byproducts, usually without any bonding material. The solidity can be improved if saw-dust, bark, wax is given to the straw as additive. Besides density, the low moisture content is that component, which gives quite favorable fuelling technical features to the briquette-pellet products.       

The pellet is a renewable bio fuelling material. The pellet has two main types:

• Wood-pellet, which basic component is the saw-dust and wood chips, coming from the clean inside part of the tree.

• Agro-pellet which is made of herbaceous plants (straw, corn, energy grass).

The ash content differs these two types of pellets in the first line. The wood-pellet has 1%-, the agro-pellet has 3-10% ash content. The wood-pellet is a more expensive fuel type, because the world’s tree stand is decreasing and because of this it is transported from a bigger and bigger distance. Agro-pellet is cheaper, because it can be produced from local agricultural products, wastages.

The plant materials, wastages, residues by agricultural production can be transformed into excellent fuels through pellet making and compressing. In contrast with wood these plants grow again from year to year and annually can be harvested, mowed.

The burning features of agro-pellets greatly differ from those of wood-pellet. The calorific value of them is much higher as well. In a lot of cases it is worth to mix the various kinds of raw materials in order to get them more compressed.

 

 Transporting, storing

Pellet can be well transported, it is a very clean fuel material. It is practical to transport them in 18-20 kg bags, or big-bags. It can also be transported in bulks. During storing, the pellets are sensitive to moisture.

3. Fire wood

The fire wood is a renewable bio fuel. Its burning cannot be such automated, like as by the granules, or grains (coal, pellet, biomass).

The fire-wood shall be stored in a dry place. The drier it is, the better calorific value it has.

The water content of the fresh-cut wood is approximately 50%. The wood – which has been stored at least for 1 year in a dry, ventilated place – contains 15-20%, this is called air-dry.

 

The wood’s firing

As we have already mentioned, the calorific value of the wood depends significantly on the moisture content. The wetter is the wood, the lower its calorific value is. The moisture shall be evaporated from the wood during combustion. As a lot of energy is needed to the evaporation of the water, the higher water content the fire-wood has, the more energy will be wastage during the heating process.

It can be well seen, that the wet wood with 50% moisture content has only the half calorific value, as a well dried wood with 10% moisture content.

According to the above table it can be stated, that it is not economic to fuel by wet wood. Related to the high moisture content the combustion temperature is lower, the soot and pollutant emission is getting bigger, and in this case the boiler’s side is getting pitched, which can be burnt in co-firing method by dry fuel.  

The remaining ash from wood firing – if it is not mixed with other material – can be spread in the garden, on the land. The wood-ash is alkalescent, it is suggested to avoid spreading big volumes to the same place.

C type boilers are available for straw- and wood firing, but they can burn practically almost everything: paper, cardboard, whole straw bales, waste wood.

The combustion chamber of the C type boilers has been designed, so that the fire-wood and waste wood with large diameter, domestic paper could be burnt.

 

Straw fuelling

Straw fuelling technologies, availability of other materials in the boilers.

• The most effective burning is the direct burning in the field of energetic use, related to international and also some domestic experiences.

• Within the direct fuelling – where the place and the receiving technology make it possible – the use of whole bales is suggested, and in a larger rate of the events it is the reasonable solution.

• Starting from the heating energy demand, and taking also into consideration the fluctuation within one year, the exact boiler type and size shall be defined in correspondence with the boiler producer, based on the available bale shape and size.

• Choosing the whole-bale fuelling technology the planning, choosing period is quite similar to the traditional, but in terms of bale-chopping, bale-cutting, automatized technologies it is very much worth to intensively cooperate with the technology supplier from the first phase of the economy-, technical planning.

• The mixed-fuelling boilers (partly straw) makes possible also the burning of wood, wood-wastage, wood-chips, and other wastages from plants, which are present in lot of cases amongst the decision-making factors.

• It is quite an admirable possibility that there are perennials, easy to “harvest” energy plants also in Hungary, and part of them can be baled, and at some of the modern „straw bale boilers” they can be burnt, related to the boiler producers’ instructions.

 

Application possibilities of straw and biomass boilers

• Application possibilities are wide range:

·         Public purchases in lower output-fields.

·         Animal plants (pig, poultry)

·         Foil and greenhouses for vegetables and flowers.

·         Heating energy supply (unique or district heating) for rural, smaller municipalities and settlements

·         Heating-, and technology energy supply for such industrial, food-industrial plants, where the site, and real-estate possibilities give the chance to fuel by straw technology.

·         In Hungary there has been started to think on a very interesting application of stawy-manure on poultry plants. It has two aims:

Use the large quantity of strawy-manure for heating aims.

The strawy-manure, which would not be used for heating at the above mentioned way, can be transformed to an easy handling, packed, natural manure.

• This culture has not yet been evolved in consumers’ minds, but a general trend can be seen all over the world, that by rapid growth of energy costs during/after economic crisis – maybe the straw is the most achievable and maintainable fuel –  the biomass fuelling is spreading very quickly and it will make its own field of industry. Both reasons are intensively present in Hungary today, so we can count with the rapid spread of straw-fuelling, particularly with regard to the more and more shortening (2-3 years, 1-2 years with applications) return of investment periods.
• The spreading of application of biomass technologies are strongly influenced by the given country’s subsidy circumstances, in which significant changes took place in Hungary in the last two years, and industry, agriculture, municipalities and private sector will have serious possibilities from the coming months. Subsidies can be read under www.szalmatuzeles.hu.
• The efficiency of planning, constructing background and the adaptability of education system. In this view the development can also be seen, though a bit slower. The – on the market present – producers have a meaningful responsibility and task in terms of education.

Periodically firing straw bale boilers

Today the market of periodically firing straw bale boilers are dominated by systems, developed for larger sizes – 1-3 cubic bales or medium sized round bales, though the smaller bale boilers also exist on good grounds. The big bale boilers are built outside, and the producer installs the combustion chamber together with heat-storing water-tank on the top, thus reducing the danger of fire.

All the periodically firing straw-bale boilers’ producer supply puffer tank as well together with the boiler, where the combustion chamber usually contains 60-80 l water/kg of straw. The calorific value of 1 kg straw is equal with 30-40 Celsius temperate increase, measured in the puffer tank, if at the same time the heat is not directed from it.

 

Automatic straw bale fuelling boilers

By automatic straw bale fuelling systems generally a maximum 20 m long bale-conveyor belt is put with bales; so the system should be filled up with bales only once a day. The conveyor belt slowly transports the bales towards the chopping unit, from where an auger or a fan moves the straw to the boiler.

Because of the continuous firing the combustion is more perfect, and the smoke gas-emission decrease is more effective. The heat transfer of the straw bale fuelling boiler is controlled by a switch on/off button, which is directed by the boiler’s water temperature sensor thermostat.

 

Burning control – one of the most important efficiency part

A modern dosing appliance, mounted with oxygen-sensor is built into the continuous fuelling boilers. Its task is to automatically fit the straw quantity to the oxygen content, measured in the smoke gas. The present volume of oxygen is measured by an oxygen-sensor – similar to the periodically firing straw bale boilers (optimally it is around 7%); this appliance regulates the quantity of the fed straw.

 The automatic oxygen volume-measure is regulated in the modern straw-bale boilers to a 5-10% efficiency growth, by the increase of the combustion’s efficiency. In the same time the CO-content of the smoke gas has decreased and also the smoke emission has decreased.

Smoke gas cleaning

The exhausting smoke gas must be cleaned in accordance with the related country’s regulations. The producers use various kinds of solutions, to which it is worth to pay attention in the planning period.

Chimney

The cleaned smoke gas is let out to the air through a chimney. Each boiler has its own smoke gas pipes. The height and diameter of the chimney, the applied technology, insulation method, etc… shall be defined in all case related to the producer’s prescriptions, by a chimney measuring program.

 

Installation proposal

The straw fuelling boilers, based on the adequate domestic or international professional know-how, development and production background, now can safely be used in Hungary.  Installation of them means serious economic advantages.

It is worth to make a feasibility study before making the decision by a professional.