Volume 27, number 3, December 2013

Conversion of biomass to natural gas, an informed decision: Case study of René Bernard Inc. dryers

René Bernard Inc. is a company that has been specializing in the production of white pine since 1966.The company has two dryers that run on natural gas. Earlier, one of the two operated as a hybrid, using biomass (75%) and natural gas (25%). However, after some major breakdowns, coupled with the competitive position of the price of natural gas on the fuel market, the owners decided to consider using natural gas for their equipment.

In order to make an informed decision, they carried out an exhaustive comparative study, taking into account several economic and operational factors: the cost and quality of the fuel, infrastructure, maintenance, and labour costs.

Cost and quality of the fuel

There is a wide variety of biofuels at variable prices and quality. The best know is wood: wood residues, sawdust, wood chips or pellets. There are also agricultural residues (straw, chopped straw, grain husks, bedding and manure), fast-growing plant species, cultivated exclusively as an energy source (willow, switch grass, miscanthus grass and poplar) and, lastly, municipal residues (prunings from trees in the park).

Since the company has its own cutting plant, it can use the sawdust produced from cutting logs into boards. This generally gives a high quality biomass with a constant humidity level. However, since the independent local production of sawdust turned out to be a huge problem, the company decided to call on a wood chip producer to fill its needs for biomass. However, that biomass had some drawbacks when it came to quality. In fact, since the humidity level of the biomass was so variable, it was suspected that it contained foreign objects, such as rocks, which caused breakdowns in the production equipment and stoppages of the biomass boiler, which, of course, entailed considerable operating expenses.

Humidity level and production cost of biomass

The humidity level greatly influences the actual production cost using biomass. Of course, the calorific value of the type of wood used is important in this calculation, but not as much as the humidity of the biomass.

The more humid the biomass, the more its calorific value is reduced. This is a linear relationship, that is, as the humidity level goes up, the calorific value goes down. What this means is that, if the humidity level is 50% the calorific value becomes 50% lower than initially, based on the net calorific value.

For example, taking into account the energy available, a customer who pays $25 per tonne for a biomass with a humidity level of 50% will see production costs doubled (i.e., $50) for that same tonne.

The calorific value natural gas, on the other hand, is always stable, both in terms of production costs and operations. In fact, the energy value of biomass has a tendency to vary, which may considerably affect the productivity of the equipment, which is not the case with natural gas.

By way of illustration, here is a fictional case that draws a parallel between biomass consumption expressed in natural gas equivalent; it shows how the energy available may significantly differ from one energy source to another.

Figure 1: Example of variation in energy available for a type of soft wood based on humidity level

Also, as Figure 2 below indicates, by precisely measuring the humidity level of each load, the actual quantity of energy available can be established and thus the profitability of operations using a biomass fuel can be evaluated.

Figure 2: Calorific value based on humidity level

Source: Fédération québécoise des coopératives forestières. L’utilisation de la biomasseforestière à des fins énergétiques, March 2012, p. 17.

So, if the price of purchasing biomass does not make an allowance for the accounting impact of the energy available, the comparison with other sources of energy is biased.

Importance of infrastructure

During the study that eventually led to the conversion to natural gas, the company examined several civil engineering considerations.

First, burning biomass requires storage space, either in a silo or, more simply, in a warehouse where the biomass will be protected from adverse weather conditions. The size of this storage space also needs to be determined, based on the capacity of the power plant, the mode and frequency of deliveries, as well as the type of fuel used.

As a general rule, there needs to be enough storage space to supply the power plant with biomass so it can run autonomously for 3-5 days at full power; provision also needs to be made for a reserve supply, depending on the reliability of the provisioning source.

Natural gas, on the other hand, is delivered continuously through an underground service line and a fixed meter. No storage facility is required.

Auxiliary energy

In all cases where biomass is used, there needs to be another a boiler operating on a different auxiliary fuel, such as natural gas, in case the biomass boiler breaks down or has to be maintained.

Figure 3: Breakdown of cost of heat with a wood-burning boiler.

Source: Biomasse Normandie

Advantages of natural gas in conversion of René Bernard Inc. dryers.

Natural gas has many other advantages over biomass. For example, in the case of the René Bernard Inc. dryers, the quality of the drying was superior with natural gas, especially since, as mentioned above, debris in the biomass chips caused frequent stoppages of the boiler. When these interruptions were lengthy, the quality of the drying was altered. In fact, during a boiler stoppage, the temperature inside the dryer dropped and, as a result, the quality of the wood was affected.

By using natural gas, the customer was able to reassign two employees full time to other duties. The customer was also able to profit from the surplus biomass. A finished product manufacturer purchased its supply of biomass chips. The company thus succeeded in generating more revenue by selling the biomass than it did when it burned it!

Lastly, by fixing the price of its supply of natural gas over the medium term, the company was able to predict its production costs.

This is just one concrete example of major savings achieved when natural gas is used in the wood-drying industry.

In conclusion, any project that calls for a choice of energies deserves a thorough study that takes into account all operational and monetary considerations in order to arrive at an efficient and economic decision for the company.

Remember that Gaz Métro has a dedicated team of sales representatives and engineers from DATECH that is available at all times to support you in your deliberations and your follow up action.

Thanks to the personnel at René Bernard Inc. who collaborated in this study.

Daniel Gendron, Eng.
Advisor, Technologies and Energy Efficiency

Article written in collaboration with:

Alain Caron, Major Accounts Representative, Eastern Québec Sales,
Gaz Métro