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Borates for Autocausticizing in Paper Production

:: Wednesday, September 15, 2021 :: Posted By Swee Hau Chew

Innovation is underway in the centuries-old paper manufacturing process.

Rising energy and chemical costs—along with stricter environmental regulations—are forcing paper manufacturers to search for new ways to reduce waste and cut costs. Chemical paper pulp mills must be open to innovative technologies to solve these challenges and elevate their sustainability efforts.

One area of production with high potential for improvement is the paper pulping process. If streamlined, this critical area can have substantial economic and environmental benefits.

Leading paper pulp mills are leveraging borates to reduce the amount of lime required and improve the chemical recovery process. And, they’re not alone. Numerous other industries have already discovered modern applications and benefits of boron.

At U.S. Borax, we have developed Neobor®, a borate product that mills can use in a new process called partial borate autocausticizing. This technology reduces carbon dioxide (CO2) emissions, energy consumption, waste, and operating costs for mills.

How pulp mills recover chemicals

To make paper, wood must undergo a chemical process to extract cellulose and produce a pulp that then can be made into paper.

More than 80% of the world’s paper mills utilize a specific type of chemical pulp production, known as kraft. This process was invented in Germany in 1884.

During the process, wood chips are digested by combining heat, pressure, and a white liquor mixture of sodium sulfide and sodium hydroxide. This causes the chips to disintegrate, leaving only the desired wood fiber (pulp) necessary to make paper. But this process also produces substantial waste. The white liquor turns to black liquor, a molten smelt of chemicals that collect at the bottom of a recovery boiler.

In the 1930s, G.H. Tomlinson discovered a method for reclaiming the spent chemicals found in black liquor. First, the smelt is dissolved in water to form green liquor. Then it’s transferred to a causticizing tank where quicklime (calcium oxide) is added to convert the solution to the reclaimed white liquor state. This causticizing process also produces a lime mud waste, which needs to be reheated or calcinated in a lime kiln to regenerate the quicklime.

While this process was innovative at the time, it’s now outdated and has two major downsides: Pollution and cost.

When burning the spent chemicals, pulp mills produce substantial CO2 and carbon monoxide (CO) emissions. And, since the process requires large amounts of lime, cost is an issue. First, the mills must purchase lime. Then, mills experience additional operating costs in restoring the lime mud waste to quicklime in a kiln.

Borate autocausticizing presents a new economical, sustainable solution

The good news for pulp mills looking to become more energy and cost-efficient lies in a technology patented by Rio Tinto (U.S. Borax's parent company): Partial borate autocausticizing. This process uses sodium metaborate (NaBO2) to supplement lime in conventional lime causticizing. The goal is to recover the sodium hydroxide necessary for white liquor without the need for a complicated regenerative process.

By using a product such as Neobor, which is an inexpensive source of sodium metaborate, pulp mills see benefits such as:

  1. Less waste and pollution: When quicklime is added in the causticization process, a lime mud is produced that needs to be regenerated or disposed. Because borate autocausticizing reduces the amount of lime needed for white liquor, less waste is produced. That also means less lime is burned in the recovery process, resulting in reduced CO2 emissions.
  2. Reduced costs: Each ton of Neobor replaces 10 to 50 times its weight in lime, saving mills money. Mills also reduce their operating costs because Neobor greatly reduces the energy used to burn lime and restore it to quicklime.
  3. Increased production capacityNeobor has been shown to increase white liquor production capacity without investing in any equipment upgrades. That results in substantial operational efficiency gains.
  4. Ease of use: Neobor requires no special equipment for loading—meaning mills can use existing equipment without additional capital expenditures. Neobor is also easy to add (depending on the mill it can be added at almost any point in the liquor cycle).

Looking ahead

Because the kraft process accounts for so much of the world’s paper pulp production, there are huge potential economic and environmental benefits from autocausticization improvements.

Even at an individual plant, there is a substantial impact. The production of a single ton of pulp results in almost 10 tons of black liquor, according to Pulp and Paper Technology. Borate autocausticization can save a plant significant money spent on materials, recovery, and energy. Over time, the positive effects multiply.

Mills around the world are seeing the benefits of using borates in chemical processes and recovery.

If your organization is interested learning more about the benefits and applications of borate solutions, contact the technical support team at U.S. Borax. We can help you evaluate whether this solution is right for your specific conditions and process.

 

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U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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