Wood pulp and paper: Water reuse drives Chinese paper mill

APP Hainan Jinhai has one of the largest paper making machines in the world.
APP Hainan Jinhai has one of the largest paper making machines in the world.
Annual production capacity is 900,000 tonnes of fine paper.
Annual production capacity is 900,000 tonnes of fine paper.
The alkaline recycling plant at APP Hainan Jinhai.
The alkaline recycling plant at APP Hainan Jinhai.
TheAPP Hainan Jinai clarifier.
TheAPP Hainan Jinai clarifier.
The treated water is then reused, discharged or used to supply an on-site pisciculture project.
The treated water is then reused, discharged or used to supply an on-site pisciculture project.

Asia Pulp & Paper (APP) Hainan Jinhai is home to one of the world’s largest single line pulp mills and the largest paper machine in the world. With an annual production capacity of 1 million tonnes of pulp and 900,000 tonnes of fine paper, APP Hainan Jinhai is a paper making facility on an unprecedented scale.

... output on this scale would be impossible without the filtration and separation systems that are also part of the process.

As the location of world’s largest paper machine – the Voith manufactured Hainan PM2 installed in 2010 – Asia Pulp & Paper Hainan Jinhai is also one of the most modern, technically advanced and efficient facilities worldwide. For example, in approximately 30 minutes the Hainan PM2 alone can produce a roll of paper 11 m in length, 3.5 m in diameter and weighing in at approximately 90 tonnes. Yet output on this scale would be impossible without the filtration and separation systems that are also part of the process.

Pulp separation

Raw logs are processed on site; the initial stage is bark stripping. The stripped logs are then chipped. Chips of an acceptable size and quality are selected and enter the pulp facility via a conveyer belt. Waste chips, residue and the stripped bark are then crushed, processed and used as biofuel in the facility’s boilers.

The accepted chips are first steamed to reach an acceptable temperature and moisture content for fibre separation. The fibre separation process at APP Hainan Jinhai is a sulphate or Kraft process. The technique employed on site involves the use of sodium hydroxide (NaOH) and sodium sulphide (Na2S), known as white liquor under heated conditions to generate a chemical reaction within the input wood chips. This chemical reaction causes the lignin, an integral part of the secondary cell wall of the timber, to fragment and dissolve into the white liquor forming weak black liquor.

The resulting pulp is then washed and oxygen bleached as the second phase of lignin removal. APP Hainan Jinhai employs a compact press as an integral part of this process. The compact press is notable for using significantly less water – 7.1 tonnes of water per tonne of pulp less than a traditional diffuser wash press.

Following the washing and oxygen bleaching process the pulp is then bleached white using an elemental chlorine free (ECF) DualD™ process.

Pulp bleaching

The four stage ECF DualD™ process is a patented chlorine dioxide bleaching process, which is performed at high temperature. 

The process combines a traditional chlorine dioxide bleaching process with a hot acid treatment in one reactor; the chlorine dioxide provides the bleaching action whilst the acid treatment attacks the remaining lignin before being removed in an alkaline filtration process.

The innovation of the DualD™ ECF process is that the chlorine dioxide and hot acid treatments are not competing processes – thus negating the need for separation. In addition, combining the two processes in one reactor has driven reductions in the level of adsorbable organic haloid (AOX) present in the effluent.

In addition to a significant reduction in the propensity of the pulp to yellow, savings in the quantity of chlorine dioxide required and the ability to create a brighter pulp when compared to more traditional ECF processes. The use of a modern ECF process significantly reduces the formation of highly toxic dioxin compounds or other carcinogenic substances through the bleaching process.

Black liquor treatment

The black liquor produced from the initial chemical separation process is first concentrated via an evaporation system before being burned in the facility’s alkaline recovery boiler. The heat from the boiler generates steam which is supplied to the facility’s steam turbine generators delivering between 70-80% of the pulp mill’s required high pressure steam volumes.

The remaining residue is then diluted to form green liquor before entering the re-cauterising process whereby the sodium carbonate reacts chemically with calcium oxide (CaO) – quicklime to form sodium hydroxide (NaOH) and calcium carbonate (CaCO3). The solution is then filtered to separate the calcium carbonate (CaCO3) solids enabling the sodium hydroxide (NaOH), which is the principal ingredient of the white liquor process, to be made ready for the next round of pulp making.

Paper making

APP Hainan Jinhai operates a variety of large production machines. However, the centrepiece is the Voith-manufactured Hainan PM2, the largest paper machine in the world – stretching for almost 600 m in length.

In addition to its size, the machine was designed to demonstrate Asia Pulp & Paper’s commitment to industry leadership in minimising the use of raw materials in the paper making process. To this end, Voith designed the machine to require the absolute minimum of virgin fibre in the paper making process by increasing the coat application (in this case mainly ground limestone). 

The machine is also an industry leader in water consumption, requiring on average 5 litres of water per kilogram of paper produced, well below the European average of 8 litres for comparable machines or the Chinese government stipulated maximum of 10.5 litres.

Water use and water treatment

The entire APP Hainan Jinhai facility was specifically designed with water conservation as a key requirement.

Water is a key component in pulp and paper making and Asia Pulp & Paper has made huge efforts to reduce its consumption and improve waste treatment.

For example, the APP Hainan Jinhai facility has employed incremental technology upgrades to reduce water consumption. The pulp facility has reduced its water consumption per tonne of produced pulp by 36% since the facility commenced operations. Filtration and separation technologies have helped to drive this development.

Whilst the most significant reduction in water use has been through the use of a compact press the facility has also employed a range of other initiatives:

  • sealing water for the mill’s pumps is collected, filtered and reused – generating a daily saving of 3,500 m3
  • water used to ‘backwash’ the cooling tower filters is now reused in the re-cauterising process to produce white liquor – generating a daily saving of 2,300 m3
  • recovery of condensed water from the steam produced by chlorine dioxide plant required for the ECF process – generating a daily saving of 660 m3
  • water condensing on the facility’s pipe racks is collected and reused in the facility’s boilers generating steam for the steam turbines and saving 600 m3 daily

In terms of wastewater, the facility treats it on-site through a three stage intensive procedure comprising chemical, biological and advanced oxidation treatments. The treated water is then reused, discharged or used to supply an on-site pisciculture project. 

The facility is currently in the process of constructing a new paper production wastewater recycling system with the capability of reusing 83% of the paper mill’s wastewater – this facility is expected to begin operations in April 2013. To date the facility’s accumulated water savings amount over 110 million tonnes of water.

Water treatment and efficiency in water management remains a strategic priority for Asia Pulp & Paper. The facility itself is located on Hainan Island which is completely separated from the Chinese mainland. When compared to mills operating in regions with more abundant water supplies, the facility is more susceptible to stoppages caused through scarcity of water. Efficient water use throughout the pulp and paper making process has therefore been a priority from day one and the company plans to make use of future advances in filtration and separation technologies to achieve even greater reductions in resource use. ♦