Chempolis

Frequently asked questions

Please, use the links below or just scroll down the page to see answers for the frequently asked questions.

Raw materials

Which raw materials are suitable for Chempolis process?
Nonwood raw materials are very bulky, is transportation a problem?
What is the availability of nonwood materials?
What is the difference between agricultural residues, energy crops and fibre crops?
If energy crops are cultivated normally for energy purposes, why should those be used for papermaking, or can they, instead of production of green energy?

Cooking

What is your cooking temperature and time?

Washing

How much does brown stock washing consume water?

Bleaching

Chemical recovery

Distillation

Boiling point of formic acid and water are very close. How are you able to separate them?

Water consumption and effluent treatment

How much water is consumed per ton of cellulose?

Chemistry

Your principal cooking chemical, formic acid, is known to be corrosive. Which materials are suitable and how does corrosion resistance affect the investment cost?

Economy

Pulp and paper

Raw materials

Question: Which raw materials are suitable for Chempolis process?
Answer: We have tested the most common nonwood materials, such as wheat and rice straw, bagasse and different reeds and grasses like reed canary grass, common reed and elephant grass. In addition, many more exotic raw materials such as oil palm biomass residues (EFB and OPF) as well as pineapple biomass have been tested. Birch and chestnut have also been tested successfully. Generally there is no restriction of raw materials as high silica content is not a problem in Chempolis process as it is in alkaline pulping technology.

Question: Nonwood raw materials are very bulky, is transportation a problem?
Answer: Nonwood raw materials are annually collected from same areas, and thus nonwood mills are smaller than wood pulp mills. Therefore process technology must be more simple and economical than in large wood pulp mills. Most of the nonwood materials are available as harvested on fields, so practically they are more easily available than wood. Typically, the moisture content of nonwood materials is 10-15 %. In addition, these materials do not have bark. For example, baled reed can have a density of 180-200 kg/m3. Therefore, transported fibre dry matter (tons) per truck is comparable to wood as cargo weight limits only wood transportation. In general, nonwood raw material transportation distances may be even higher that 200 km. It is also worth mentioning that there are many nonwood raw materials, which are already at mill gate like bagasse and oil palm residues.

Question: What is the availability of nonwood materials?
Answer: Nonwood raw materials are available in abundance worldwide. More than 2 400 million metric tonnes of nonwood materials are available annually, which could yield more than 1 000 million tonnes of paper. This is three times today's global annual paper consumption (350 million tonnes). The availability of nonwood materials is shown on Nonwood Resources page.

Question: What is the difference between agricultural residues, energy crops and fibre crops?
Answer: Agricultural residue crops are the waste part of plants used typically in food production. Energy and fibre crops, sometimes called also as on purpose crops or industrial crops, are cultivated usually only for non-food production, e.g. for energy or papermaking purposes. Typical agricultural residue crops are wheat straws, rice straws, bagasse (sugarcane waste) and corn stalks. Common on purpose crops are for example Elephant grass / Miscanthus, reed canary grass or kenaf.

Question: If energy crops are cultivated normally for energy purposes, why should those be used for papermaking, or can they, instead of production of green energy?
Answer: In some cases production of green energy by using energy crops is not viable enough without subsidies. By using energy crops in Chempolis process, all parts of the plant fibres can be used in the most efficient way. Plant fibre raw materials consist of cellulose, hemicellulose and lignin (the glue-like part of the fibres). In papermaking process, only the fibres, i.e. the cellulose containing part, are needed to produce high-quality pulp and paper products. The leftover part, i.e. dissolved hemicellulose and lignin, can be used in green energy production. By doing this, profit per ton of raw material is many times higher than in energy-only production.

Cooking

Question: What is your cooking temperature and time?
Answer: We apply only mild temperature, which is slightly over the boiling point of cooking liquor. This is to eliminate the current risk of backflow in feeding of digester and to save energy and investment in cooking. Cooking time is typically 20-30 min.

Washing

Question: How much does brown stock washing consume water?
Answer: The intake of fresh water is around 3.5-4.0 t/ADt (pulp), depending on the applied washing technology. Washing consumes only minor amounts of fresh water, because the water in washing filtrates is recovered and returned back to the process.

Bleaching

Question: On your publications it is stated that very high brightness values are achieved by using only hydrogen peroxide as bleaching chemical. How is this possible? This is not possible in conventional systems.
Answer: It is true that hydrogen peroxide reacts poorly with typical alkaline cooked straw pulp. In Chempolis process residual lignin groups are modified in cooking so that they are reactive towards oxygen-based bleaching. One major advantage is also the fact that in acidic cooking conditions metal-ions (Fe, Cu, Mn, Co) present in raw material are dissolved and removed, thus they do not enter into bleaching and disturb reactions.

Question: How bright pulp can be produced from nonwood raw materials?
Answer: Nonwood raw materials are somewhat more difficult to bleach than for example hardwoods. Brightness target is set according to customer needs. For example, we have achieved ISO 90-92 % brightness for reed. Wheat straw has been bleached to ISO 85 % brightness, which is more than with current corresponding pulps and general requirements.

Chemical recovery

Question: How do you recover the cooking chemicals?
Answer: Our principal cooking chemical, formic acid, is a volatile compound and it can be recovered using conventional thermal separations such as evaporation and distillation.

Question: How does the evaporation work?
Answer: Most of the acid is recovered directly in evaporation. Formic acid vaporises and is recovered as evaporation condensates. Therefore, evaporation is not only a chemical recovery process but also a concentration process for dissolved material.

Question: How do you avoid scaling of evaporators?
Answer: Silica, which is present in nonwood raw material, does not dissolve into cooking liquor in Chempolis process. Evaporation of liquor is similar to evaporation of wood black liquor. Another advantage is also the fact that there is no sodium in black liquor and thereby no solubility limitation on sodium.

Question: How much of the formic acid can be recovered? What is the consumption of make-up formic acid?
Answer: Recovery rate of formic acid is over 99 %. In addition, some formic acid is generated from raw material. Therefore process is almost self-sufficient in terms of cooking chemicals.

Distillation

Question: Boiling point of formic acid and water are very close. How are you able to separate them?
Answer: There are several technical solutions. One is to use elevated pressure in distillation, just like in commercial production of formic acid. Another solution is to use extraction distillation.

Water consumption and effluent treatment

Question: How much water is consumed per ton of cellulose?
Answer: Chemical and water cycles can be fully closed in Chempolis process. Therefore, the water consumption can be nearly zero. However, in practise, environmental regulations allow some usage of water. Most customers have set the consumption to 10 m3 of fresh water per metric ton of pulp. This can be achieved easily.

Chemistry

Question: Your principal cooking chemical, formic acid, is known to be corrosive. Which materials are suitable and how does corrosion resistance affect the investment cost?
Answer: Main construction material of the process is carbon steel, following stainless (AISI 304) and acid proof (AISI 316) steels. In more corrosive conditions, duplex grades are used. Only about 1 % of piping material has to be more corrosion resistant than previous grades. The additional cost of "corrosion resistant" materials is minor in pulp mill project.

Economy

Question: The capacities of new greenfield pulp mills have increased to one million metric tons per year to meet the demand of economical production. What is the minimum capacity of economically viable nonwood pulp mill?
Answer: Depending on the price of raw material and the location of mill the minimum mill size is 30 000-50 000 Adt/a.

Question: How much are the operating costs? Which are the main costs?
Answer: Operating costs are mainly raw materials costs. The cost of chemicals is rather small thanks to efficient chemical recovery. In addition, energy costs are not significant as dissolved dry solids, e.g. lignin and hemicellulose, are combusted, which generates the energy needed in process.

Pulp and paper

Question: What paper grades can be manufactured?
Answer: Chempolis pulp is suitable for all paper and board grades. Chempolis process can also be used to manufacture dissolving pulp.

Question: Nonwood materials are typically short fibrous, what is the strength of paper?
Answer: Nonwood fibres have very good bonding properties and their volume is high, so the strength is above 50 Nm/g, which is enough also for high speed paper machines. Due to good bonding properties, need for refining nonwood pulp is minimal. There are also available nonwood plants, which have much higher fibre length than in wood. Therefore, high quality tree free papers are reality.

Question: Can papers manufactured from non-wood fibres be recycled?
Answer: Yes, they can be recycled. In general, there is no big difference between tree-based and tree free papers in this case.

Question: Is it possible to produce dissolving pulp with Chempolis process?
Answer: Yes, it is. With Chempolis process it is possible to control the hemicellulose content quite easy, which is important in dissolving pulp production. We have done research work also in this area and tested for example viscose manufacture.

Question: It is mentioned on your web pages that wheat straw is a high-quality raw material for papermaking, although for example in China wheat straw pulps are regarded as devalued products?
Answer: It is notable that chemistry of Chempolis process differs from conventional alkaline pulping processes. Therefore, pulp can be bleached to higher brightness by using TCF-sequence, while maintaining also the strength properties. Thus, the process is very important beside the raw materials, which, on the other hand, define many features of pulp, for example fibre length and length distribution.