Modern pulp mills rely considerably on Medium Consistency (MC) processes to minimize water usage and bleaching chemical consumption. The higher viscosity of MC pulp requires technology and equipment specifically designed for mixing, transporting, and handling pulp at MC conditions throughout the fiberline – saving water, energy, and equipment.
Reducing unnecessary dilution, saving energy, and reducing the amount of equipment required are all sound reasons to maintain higher consistencies throughout the fiberline. ANDRITZ MC equipment is utilized at key positions throughout the fiberline to ensure that the advantages of MC pulping are maintained throughout the entire process. Efficient mixing and effective air removal is key to success.
The efficient and thorough mixing of bleaching chemicals with the pulp is key to pulp quality. Proper mixing provides homogeneous bleaching conditions, reduces consumption of chemicals and energy, improves product quality, and reduces environmental load. ANDRITZ AMix AC chemical mixers are designed for mixing both gaseous and liquid chemicals in MC conditions. The ANDRITZ AMix AZ is designed specifically for ozone bleaching.
When MC pulp is pumped, a plug flow of pulp is generated in the pipeline. To maintain flow while avoiding “channeling” as the pulp is pumped into large reactors for bleaching, the pulp feed must be uniformly divided across the entire diameter of the reactor. This is best accomplished with an ANDRITZ AFlow ARF reactor feeder. The AFlow ARF fluidizes the pulp to create flow characteristics similar to water, ensuring smooth feeding that is clog-free.
When MC pulp is discharged from a pressurized reactor typically found in oxygen delignification and some bleaching processes, there is again the potential for plugging and channeling. That is why ANDRITZ designed the AFlow ARD reactor discharger. The AFlow ARD is equipped with gas removal capability, which has proven to be beneficial in oxygen-based bleaching processes.
The AFlow ATF tube fluidizator was developed especially for the dilution of pulp from MC to lower consistencies required in the screen room (2.5 – 5%). The arrangement of the AFlow ATF in the screen room feed tank is compact and provides an accurate, uniform feed consistency to the screens. It is also very energy efficient.
Due to the viscosity of the pulp, scrapers are required in MC or high consistency stock towers and in atmospheric reactors in the bleach plant. The ANDRITZ ADS scraper is designed for the bottom of a stock tower to prevent pulp channeling and ensures even discharge. The ADS works by scraping the stock over the entire bottom area and directing it to the suction opening of the discharge pump.
For bleaching applications, the ANDRITZ ATS top scraper ensures uniform, disturbance-free discharge of pulp from an atmospheric pressure tower. Models are available for either low consistency (ATS-LC) or medium consistency (ATS-MC) discharging. The ANDRITZ ATS discharge scraper produces a continuous and stable discharge flow from the bleaching tower, making it possible to directly feed a washer without the need of intermediate tanks, pumps, or transfer screws.
