Development of recovery boiler technology
Abstract and Figures
Recovery technology developed from early inefficient chemical recovery to modern large plants. Early rotary units had to fade when new larger and more reliable units came were available in the 1930's. Changes in investment costs, increases in scale, demands placed on energy efficiency and environmental requirements are the main factors directing development of the recovery boiler. This has resulted in use of higher steam parameters and black liquor dry solids. An example modern Scandinavian mill produces more than 30 MWe for sales with annual pulp capacity of aboot 600 000 t/a. Already net revenue of around 10 % can be achieved with surplus electricity, bark and wood residue sales. This amount can further be increased with adoption of utility type power plant connections. Size of pulp lines has increased. In the largest lines we talk about utility sized power production (>100 MWe). Economics of scale means there are currently new economic possibilities to increase the yield of bioenergy.
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... Additionally, using Tomlinson recovery boilers to treat straw black liquor (SBL) is more difficult because of the high silica and chlorine contents, high viscosity and low heat value of SBL [7][8][9]. For these reasons many researchers have focused on developing alternative BL recovery technologies [10][11][12]. These technologies include: supercritical water gasification [13][14][15][16], hydrothermal treatments [17][18][19][20][21], hydrolytic methods [22], activated carbon production [23], biochar production [24,25], organic compound production [26,27], biofuel production [28,29], as well as microbial electrochemical treatment [30], and flocculation [31]. ...
Fluidized bed pyrolysis is a promising technology for recovering value from reed black liquor (RBL) but it can be limited by agglomeration of the bed material and loss of fluidization. To address this challenge, laboratory experiments examined the continuous, fluidized bed pyrolysis of RBL using two different bed materials at temperatures ranging from 530 to 780°C. Pyrolysis with silica sand as the bed material showed sintering within 120 s and loss of fluidization at a bed temperature of 680°C. Pyrolysis with calcium-based zeolite as the bed material retained fluidization for the entire test period of 30 min at all temperatures examined. Increasing pyrolysis temperature with the calcium-based zeolite increased H2 generation and decreased tar production, with the highest temperature examined (780°C) providing the best performance. Fluidized bed combustion of the pyrolysis char (both at 780°C) recovered 87% of the sodium in the RBL. Pyrolysis of RBL using fluidized bed technology with a calcium-based zeolite bed material is feasible and effective.
The paper first examines the reults of laboratory and field studies of the sintering characteristics of deposits and precipitator dusts collected from various recovery boilers. Then the effect of sintering on the boiler plugging is explored. Sintering of deposits and dust begins at temperatures as low as 300 degree C. In the range of 500 degree C to 600 degree C, deposits sinter rapidly, reaching a maximum strength in less than 1 hour.
The two common types of recovery boilers are the Combustion Engineering-type (CE) and that of Babcock and Wilcox (B&W). There are two basic concepts for spraying the liquor. One concept, typical of CE-type recovery boilers, is to spray black liquor into the furnace and allow the liquor droplets to descend through the upflowing combustion gas. The other concept, typical of B&W-type recovery boilers, is to spray the liquor on to the furnace walls. While these concepts underline the basic design, the actual practice in a given furnace is a combination of the two.
This book details advances in the production of steam and the utilization of all types of fuels. Section 1 covers Steam Fundamentals including thermodynamics, fluid mechanics, heat transfer, boiling heat transfer/two phase flow/circulation, metallurgy/materials and structural design. Section 2 covers Steam Generation from Chemical Energy. Section 3 covers Applications of Steam. Section 4 covers Environmental Protection. Section 4 covers Specifications, Manufacturing and Construction. Section 6 covers Operations. Section 7 covers Maintenance and Life Extension. Section 8 covers Steam Generation from Nuclear Energy. Finally, Section 9 covers Balance of Plant. With 57 chapters, over 1100 figures, hundreds of tables and hundreds of references, this book comprehensively covers modern Steam Generation technology. Copies of this copyrighted material are available from www.babcock.com .
Lower sulfur emissions at a pulp mill result in higher sulfidity levels and in the enrichment of potassium in the mill`s liquor system. The sulfidity values at Scandinavian kraft mills previously fluctuated between 28 and 35%; today they exceed 45%. Viscosity measurements show that the viscosity decreases drastically when the sulfidity increases from 30 mole% to 40 mole%, its potassium and chlorine levels are high enough, and the char bed is low, the smelt flows easily and may penetrate the char bed, approaching the floor tubes. In extreme cases, the hot smelt destroys the layer of solidified smelt on the floor tube`s surface and reacts very rapidly with the floor tube.
The strongest driving force in the pulp industry is the environment. New process equipment has been installed to reduce emissions and chlorine usage. Recently, more attention has been paid to mill closure. Some of the promising new technologies are waste-water evaporation, green-liquor clarification and thermal-heat-treatment of black liquor. Black-liquor gasification requires more materials technology research. The best way to new meet demands is to modernize the basic process step by step, one unit at a time.
A new solution to third generation chemical recovery
- Rolf Ryham
Ryham, Rolf, 1992, A new solution to third generation chemical recovery. Proccedings of
1992 International Chemical Recovery Conference, Seattle, Washington, June 7-11, pp. 581
-588.
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New developments in recovery unit design
- Frank W Hochmuth
Hochmuth, Frank W., 1953, New developments in recovery unit design. Tappi Journal,
Vol. 36, No. 8, p. 359.