Power and recovery

The Acrobat PDF documents below are white papers in the Valmet Technical Paper Series related to power and recovery. You may download as many papers as you like, simply by clicking on the white paper name in the Download column.





Biosludge Disposal in Recovery Boiler



Biosludge is the most problematic residue of the effluent treatment process when it comes to disposal. The high moisture content makes it difficult and costly to landfill or to incinerate in a power boiler. A proven new disposal method is discussed in this article - hydrolyze the secondary sludge and mix it in the black liquor at the evaporators to burn it in the recovery boiler.


Evaporator and Recovery Boiler Energy Efficiency



The white paper presents a study which reviews current practices in the design of new evaporators, how these design practices have changed in the past 30 years and how upgrading older evaporators can help the mill achieve most of the benefits associated with the more current practices. The white paper concludes with a case study which helps understand what can be done to increase the energy efficiency of an existing recovery boiler and explains how the boiler performance is affected.





Using Valmet's bio-gasification technology, a plant can reduce the use of fossil fuels by close to half and reduce CO2 emissions. Another possible potential is turning a fluidized bed boiler at a power plant into a bio-refinery incorporating pyrolysis technology. Finally, Valmet is focusing on developing processes and equipment in three main areas where the end products are second-generation bio-based transportation fuels, chemicals and materials via concentrated acid hydrolysis of biomass and green coal.


Minimizing Environmental Impact 



Valmet's products and services reduce the environmental load and improve the quality of mill operations. Examples include: effective water management, GreenSound silencers for use in urban mills, minimizing CO2 emission, and sustainable energy production with bubbling fluidized bed conversions.


Working Towards a Safer Recovery Boiler Operation



Valmet has developed and perfected several auxiliary devices that serve to both automate as well as either remove the need for direct operator involvement or to minimize exposure to unsafe working conditions. This paper will provide an overview of the development of these products and their applications for improving operator safety, as well as actual return on investment they bring by making the operation of the boiler more stable.


Paper mill boiler chemical cleaning - why, when and how? 



A pulp and paper mill's operation requires that its boilers operate reliably and efficiently. Excess deposits within boiler tubes can cause failures of the tubes, which not only result in lost production, but can also place mill personnel and equipment at risk of injury and damage. This paper addresses how deposits affect boiler reliability and efficiency and analyzes what makes a good boiler cleaning program.


High power generation from recovery boilers - What are the limits?



The energy efficiency of modern recovery boilers, such as Äänekoski, can be improved by introducing high power features. Particularly important are the effect of ash composition and ash treatment.


XXL size recovery boilers - status and prospects



XXL size recovery boilers have operated quite well and their availability has been good. These boilers are able to burn many kinds of fuels without increasing their emissions. Valmet has delivered many boilers with the capacity of 4000-5000 tds/d. Experiences from those references have been extremely important when developing larger boilers, such as the XXL units. The latest achievement is the delivery of a new XXL size high-power recovery boiler to Äänekoski, Finland.


Odorless pulp mill in operation



Valmet has delivered a unique, practically odorless mill to CMPC Riograndese Ltda in Guaíba, Brazil. The design guidelines were to not vent odorous gases and to aim for zero smells. The gas handling system collects and controls odors from more than 100 sources and all process areas are included. Incineration of non-condensable gases is ensured through multiple, simultaneously available incineration locations.



Circulating fluidized bed evolution from coal to biomass



Valmet has been developing and delivering circulating fluidized bed (CFB) boilers for over 30 years. There has been a huge evolution in CFB technology, especially in customers’ technical demands and also in emission requirements. In the 1980s CFBs were only coal firing equipment, today they are real multifuel firing equipment, and sometimes even 100% biomass boilers. This paper examines their evolution using real project examples together with lessons learned, and speculates on upcoming improvements.


Recovery boiler SCR



SCR – Selective Catalytic Reduction is a well-established and widely used technology for NOx removal from power boiler flue gases. Target emission levels are decreasing and SCR will soon be needed for recovery boilers. This paper presents a study for a retrofit case using SCR to lower NOx from 200 to 100 mg/m3 (6% O2, dry gas), including implementation of some high power features.


The Modern White Liquor Plant



The growing trend of a resource efficient and clean world strongly impacts white liquor plants worldwide. Process impact is evaluated when using green liquor filtration and clarification technologies. Methods to mitigate the impact of different strategies of lime cycle management are discussed. Reducing carbon footprint by substituting oil with biofuel and the potential pitfalls are reviewed.


Controlling Sulfidity in a Modern Kraft Pulp Mill



In order to reduce sodium make-up and at the same time increase the capacity to receive sulfur rich side-streams, a new process for generation of sulfuric acid from non-condensable gases has been introduced. The acid replaces intake of sulfur to the process and thereby creates a better balance which reduces the need for make-up sodium.


Recovery Boiler Optimization - Reduction Rate Control



A recovery boiler’s main control variables of reduction rate were studied and the performance of the Valmet Recovery Analyzer’s online reduction rate measurement was evaluated in real recovery boiler conditions. The main objectives were to examine which control variable had the most significant effect on reduction rate and to find out how well the analyzer worked under changing burning conditions.


Next Generation LignoBoost



The number of products that can be made from lignin continues to increase. This paper looks at the development of add-on processes to produce tailor-made lignin, which includes the possibility of creating completely odorless biocomposite end products.


Improved Recovery Boiler Cooling and Washing Practices



In many cases the length of a mill outage is set by the time needed for recovery boiler cooling, washing, inspections and repairs. The ways cooling and washing are carried out can be optimized so that the total outage time can be reduced.


Expansion of recovery capacity at Södra Cell Väro



The massive upgrade of the Södra Cell Värö mill in Sweden has increased the mill's capacity by 64%, with a new maximum of 700,000 ADMT/year of Northern Bleached Softwood Kraft. This paper reviews changes made to the evaporation and chemical recovery boiler area.


HOFOR moves toward CO2 neutrality by utilizing the capabilities of CFB



Denmark's largest utility company, HOFOR, erected a new power plant in Amagervaerket  Copenhagen. It is a big step toward the CO2-neutral Copenhagen targeted by 2025. The HOFOR BIO4 project is a showcase in how to change fuel from coal to biomass in large power plants. CFB technology allows the use of biomass with very different properties – in this case the moisture content can vary from 25% to 60% (calorific value 6–14 MJ/kg). That offers a lot of freedom in fuel supply and cost-effective fuel.


Methanol, from waste byproduct to valuable fuel



This white paper reviews the technology that has already been used for several years to liquify methanol from the SOG and the new process that has been developed to produce purified methanol that can be sold as a green renewable fuel, transforming an undesirable waste byproduct into a potential new revenue stream for the pulp mill.


Using wood powder as fuel in lime kilns



This white paper discusses the use of wood powder as a replacement lime kiln fuel, as well as the factors that must be considered when evaluating using wood powder as kiln fuel and the lessons learned from operating with wood powder. The Södra Värö mill with a wood powder firing system installed in 2014 has contributed their experience to this paper.


Recovery boiler floor protection



For recovery boilers, optimizing both the floor protection methods and materials and the cooling, washing and cleaning practices can yield significant savings in mill outage time and corresponding increases in mill production and reduced risk of mechanical damage due to mechanical cleaning or hydro blasting during floor cleaning.


Production of sulfuric acid from pulp mill NCG - a biorefinery concept



Production of sulfuric acid from pulp mill non-condensable gases enables the bioproduct mill to become nearly self-sufficient in sulfuric acid usage. Sulfate led to the mill's effluent treatment plant is reduced and the sulfate load to nearby waterways is decreased drastically. Reduces purchasing by 350 truckloads of sulfuric acid per year.


Evaporator issues and technology


Evaporators are used to evaporate black liquor from approximately 15% dry solids to 70-85% dry solids. Operating issues include scaling, corrosion, liquor carry-over, vacuum, condensate segregation and foaming liquor. Each can be mitigated with process and technology changes.