| 1. |
- Jansson, Johan, et al.
(author)
-
Model based control and optimization of continuous digester
- 2008
-
In: TAPPSA Journal.
-
Journal article (peer-reviewed)abstract
- Continuous pulp digesters are large reactors with significant residence time. They play a critical role in shaping the pulp qualities achieved at the product-end. For this reason, there is a big drive towards developing fundamental dynamic models to be used for better process understanding and control (especially in the development of model based controllers).In this paper we discuss the use of physical models for diagnostics and process optimization of a continuous digester. Accurate diagnostics are not possible without the use of a pressure-flow net. The pressure-flow net also makes it possible to validate pressure and flow sensors in the circulation around the digester. For control purposes however, the pressure-flow net is not so important. Two dynamic physical models were built for a continuous digester, one with a pressure-flow net and one without. The model without the pressure-flow net has been tuned and tested with good results at Ngodwana mill. It was not possible to get the model which included the pressure-flow net running with as many digester section blocks as we wanted due to the he system becoming stiff. However, for a lower number of sections results were obtained. With an adjustment of the boundary conditions, higher number of sections should be possible to test as well.
|
|
| 2. |
- Jansson, Johan, et al.
(author)
-
On-line simulation of continuous pulp digester
- 2009
-
In: TAPPSA Journal.
-
Journal article (peer-reviewed)abstract
- Continuous cooking is the dominant process in the kraft pulping industry. Our general knowledge and understanding of process conditions inside the digester is limited. Process control systems comprise of groups of measurements, which give information about conditions at the outer shell of the digester. These measurements mostly tell about cooking liquor inflows and outflows, temperature and it is also possible to measure pressure or pressure difference at the screen section of the digester shell. But ultimately process conditions inside the digester are based on measurements at the shell and intelligent approximations. The aim of this paper is to describe more accurately the cooking conditions and phenomena inside the digester. A model of a continuous digester was developed as an extension of the well known Purdue model [Bhartiya, 2003]. The model was adapted to simulate an industrial Lo-Solids pulp digester as well as an ITC digester. The models were then used to do online predictions and these predictions were compared with the actual plant performance.
|
|
| 3. |
- Naqvi, Muhammad, et al.
(author)
-
Polygeneration system integrated with small non-wood pulp mills for substitute natural gas production
- 2018
-
In: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 224, s. 636-646
-
Journal article (peer-reviewed)abstract
- This study aims to examine the potential substitute natural gas (SNG) production by integrating black liquor gasification (BLG) island with a small wheat straw-based non-wood pulp mills (NPM), which do not employ the black liquor recovery cycle. For such integration, it is important to first build knowledge on expected improvements in an overall integrated non-wood pulp mill energy system using the key performance indicators. O2-blown circulating fluidized bed (CFB) gasification with direct causticization is integrated with a reference small NPM to evaluate the overall performance. A detailed economic analysis is performed together with a sensitivity analysis based on variations in the rate of return due to varying biomass price, total capital investment, and natural gas prices. The quantitive results showed considerable SNG production but significantly reduced electricity production. There is a substantial CO2 abatement potential combining CO2 capture and CO2 mitigation from SNG use replacing compressed natural gas (CNG) or gasoline. The economic performance through sensitivity analysis reflects significant dependency on both substitute natural gas production and natural gas market price. Furthermore, the solutions to address the challenges and barriers for the successful commercial implementation of BLG based polygeneration system at small NPMs are discussed. The system performance and discussion on the real application of integrated system presented in this article form a vital literature source for future use by large number of small non-wood pulp industries.
|
|
| 4. |
- Porian, Bijan, 1962-, et al.
(author)
-
Modelling of the Chemical Reactions in a Continuous Pulping Digester in the Presence of the Channelling Phenomenon
- 2009
-
In: International Review of Chemical Engineering Rapid Communications. - Naples, Italy : Praise Worthy Prize. - 2035-1755. ; 1:5, s. 419-427
-
Journal article (peer-reviewed)abstract
- Pulping digester including the channelling phenomenon and chemical reactions in the channel is modelled using the CFD, finite volume method, FLUENT. The objective of this paper is to predict the chemical and hydraulic behaviour of the digester under the hazardous situations.A 2D geometry of the digester is built and symmetric planes are defined in the Gambit. The mesh is then exported to the FLUENT and then the created half geometry was treated by axisymmetric function to establish a complete model of the digester. The Eulerian scheme is applied which represent the multiphase flows in the digester. A heterogeneous porous media is defined for the compressible bed. Species transport is applied to define a mixture template of the wood chips components. The kappa number is predicted in the channel and around it to characterize the cooking development under hazardous conditions.
|
|
| 5. |
- Pourian, Bijan, 1962-, et al.
(author)
-
CFD modelling of solid-liquid multiphase and mathematical separation of the phases in a continuous pulp digester
- 2010
-
In: International Journal of Modelling and Simulation. - : ACTA Press. - 0228-6203. ; 30:3, s. 384-395
-
Journal article (peer-reviewed)abstract
- This paper describes the use of a CFD multiphase model using commercial FLUENT software to aid understanding of the physical behavior of solid and liquid flows in the digester of the pulping process. We take into consideration the mass balance of the multi-inlets, outlets and circulation flows in the digester. We also look at the application of a Porous media model to describe the dynamic behavior of the liquor flow through a bed of solid particles.The cylindrical Korsnas/vallvik pulping digester in Sweden is represented in the models as an axisymmetric two-dimensional model, which includes multiple feeds, outlets, pressure adjustment valves and circulation pipes.Separation of the phases is an important part of the pulping process. A number of multiphase models are evaluated for their potential use in phase separation.For this evaluation we constructed the two-dimensional digester model in the Gambit software package, a pre- processor tool for FLUENT Physical strainers at the entrances of outlet pipes were designed in Gambit, in order to investigate the possibility of physically separating large solid particles from the liquid flow where both phases are subject to suction into the circulation pipes.The compaction of the wood chips is also considered in the modeling. In the Porous model, the digester is divided into sections of different porosity, and the behavior of individual suspension particles is not considered. The bulk of this paper concerns modeling mass balances and phases of the mixture in the digester using Eulerian and Mixture strategies.
|
|
| 6. |
- Pourian, Jan, 1962-, et al.
(author)
-
Modelling of the channelling phenomenon of the pulping digester using porous Media
- 2009
-
In: <em>SIMS, Scandinavian Modelling and Simulation Society 50, conference in Fredrice, Denmark, October 7-8 (2009)</em>. - Fredrice : SIMS electronic.
-
Conference paper (peer-reviewed)abstract
- A dynamic model is developed for a continuous pulping digester to characterize the channeling phenomenon. The commercial CFD codes, FLUENT, are used to compute the hydraulic behavior of the digester under the normal and particular operational conditions. All the circulation flows, extractions, multiple inlets and outlets are included in this model. The digester is designed in the Gambit and an axisymmetric 2d model is applied. A porous scheme is implemented in the model in order to design the fluid flow and channelling phenomenon inside the digester. A heterogeneous porous media is specified in order to take the compression of the pulp into account. The simulation can serves as a prognosis model to predict the risk situations and probably to hinder high economical damage. The k- model contributes to compute the flow “regimes” or eventual eddies in some turbulent zones of the digester.
|
|
