Kraft Pulp & Paper Industry: Heat Exchanger and Heat Recovery System
Heavy Liquor Heater
Heat exchangers for heavy liquor include a shell and tube heat exchanger using indirect steam to heat liquor within the tubes. Liquor re-circulation is utilized to maintain velocity within the heat exchanger at varying boiler operating rates.
Options available include the use of Reynolds enhanced heat transfer (REX) technology. REX inserts are spiral blades inserted through the length of each tube of the heat exchanger to promote turbulence at lower fluid velocities. Benefits include reduction in pumping horsepower by as much as 45% and improvements to fouling and scaling resistance. Inclined horizontal position or vertical installations are available. A specialized water bath de-superheater is included in the system to provide fully saturated steam the the heater under all operating conditions.
Batch Blow Heat Recovery
The collection of the non-condensable gas (NCG) from the digester blow requires the efficient condensing of the blow vapours without relief to the atmosphere or the intake of ambient air into the system. The batch blow releases a large amount of heat in a short time resulting in a high condensing water demand, thus most systems are direct contact condensing.
A.H. Lundberg’s batch blow heat recovery systems are designed to take a batch process and turn it into a continuous heat source. Our system will include pressure and vacuum relief devices, a cyclone separator for removal of entrained fibre, a direct contact primary co-current condenser, an accumulator tank, an indirect secondary condenser, heat recovery heat exchangers, and a condensing water supply pump.
Vent Gas Heat Recovery
Vent gas heat recovery system (HRS) provides high efficiency heat recovery from an industrial plant’s waste gases normally vented to atmosphere. The simple process includes an indirect co-current condenser to recover the heat from flue gases into a glycol solution, a glycol recirculation system, an induced draft fan and stack, an acid condensate handling system and auxiliary heat exchangers to utilize the captured heat. The system is applicable to flue gas as well as hot and wet gases vented from process operations.
Batch Digester Liquor Heater
Heating the cooking liquor using external, indirect heat exchangers gives improved operation and reduced variability of the digester operation. Our digester liquor heaters are vertical arrangement heat exchangers specially designed to tolerate repeated thermal and hydraulic shock inherent in these services.
Kraft Continuous Digester Heat Recovery
For continuous digester systems, the heat is recovered from extraction liquor flash tanks and the steaming vessel. In mills pulping softwood, the continuous digester heat recovery system serves as the first stages to turpentine recovery. Fiber is removed from the vapor using a cyclone separator and then the vapor is condensed either directly or indirectly. The AHL design is two-stage system with the first stage being a co-current direct contact condenser and the second stage is a counter-current shell and tube unit.
Chlorine Dioxide Solution Heater
AHL recommends the use of heater exchangers to optimize energy consumption in the bleach plant to reduce energy cost by using hot effluent to heat the chlorine dioxide solution.
Our bleach plant chlorine dioxide solution heater is used to exchange heat between chlorine dioxide solution and extraction stage filtrates. This reduces the steam demand in the bleach plant needed to reheat pulp in the bleaching tower cooled by cold bleaching solution. As the chlorine dioxide solution is warmed by extraction stage filtrate, the filtrate temperature to the effluent treatment system is cooler, reducing problematic high temperature loading of effluent to the treatment system. Shell and tube units are provided for this service, installed in a slightly inclined horizontal position, to accommodate safe removal of any gases possibly released from the chlorine dioxide solution.
AHL supplies surface condensers for many different types of vapour and operating conditions. Our experience includes the design and supply of dirty steam condensers, foul condensate condensers, reflux condensers, organic vapour condensers, and condensers containing high percentages of non-condensable gases. Condensers may be designed on a “stand alone” basis or be integrated into a mass transfer column. Horizontal and vertical orientation designs are given consideration.
Thermo-Mechanical Pulping (TMP) Industry: Heat Recovery System
Heat recovery from a TMP plant is available at a number of different levels depending upon a given mill’s process and heat utilization requirements. AHL brings decades of experience to properly implement these systems returning maximum benefit from the chosen technology.
TMP Refiner Heat Recovery (Atmospheric)
In many plants refiners are operated at low or near atmospheric discharge pressures and generate contaminated steam, often vented to atmosphere. This heat may be recovered as either hot process water using shell and tube condensers or as hot process condensate using direct contact condensers.
AHL provides both direct and indirect heat recovery systems, designed to resist fibre fouling and provide high efficiency heat recovery from the vent steam. Additionally, the systems are applicable to steam vented from stock chests containing large amounts of air.
TMP Refiner Heat Recovery (Pressurized)
Thermal Mechanical Pulp (TMP) refiners may be operated at elevated pressures and blow their pulp at these pressures generating contaminated steam. This steam can be recovered as clean steam at a slightly reduced pressure using a falling film reboiler.
The contaminated steam is directed to condensing service on the tube side of the reboiler. Boiler feed water is circulated on the shell side, falling down the outside of the tubes and generating clean steam. Heat recovery generally exceeds 96% thermal efficiency. Clean steam generation is designed to achieve discharge pressures within 5-7 psi of the contaminated steam inlet pressure to the reboiler.
The AHL design incorporates a venturi scrubber and wet cyclone into the reboiler, minimizing the impact of fiber carry-over and reducing fouling to a minimum. As a result, our TMP heat recovery systems have operated continuously in excess of many years without the requirement of shutting down for off-line cleaning.
See other equipment that we offer for the pulp and paper industry.