| 1. |
- Hahn-Hägerdal, Bärbel, et al.
(författare)
-
Production of ethanol from lignocellulosic materials
- 1988
-
Ingår i: Animal Feed Science and Technology. - : Elsevier BV. - 0377-8401. ; 21:2-4, s. 175-182
-
Tidskriftsartikel (refereegranskat)abstract
- In the bioconversion of lignocellulosic materials to ethanol, the cost of the raw material and the cost of the enzymes have been identified as the major costs for the product. In addition, many lignocellulosic materials contain considerable amounts of five-carbon sugars which are not easily fermented to ethanol. The possibility of improving the cost-intensive steps was investigated. The steam pre-treatment of a fast-growing species of Salix (Q082) was optimized with respect to treatment time and temperature, to give the best glucose yield after enzymatic hydrolysis. It was found that the semi-continuous production of cellulolytic enzymes with Trichoderem reesei Rutgers C30 in an aqueous two-phase system (an extractive fermentation system) increased the amount of recoverable enzyme activity compared with a batch process. It was also found that the enzyme consumption in the hydrolysis of cellulolytic materials, in filter paper units (FPU) g−1 reducing sugars (RS), could be considerably reduced by recirculating the cellulolytic enzymes in an aqueous two-phase system combined with an ultra-filtration unit. For the fermentation of pentoses, it was found that the combination of the commercial enzyme glucose isomerase and regular bakers' yeast, Saccharomyces cerevisiae, was superior to xylose fermenting yeasts. Yields and productivities comparable to those obtained in hexose fermentation could be achieved.
|
|
| 2. |
- Larsson, L, et al.
(författare)
-
The measurement of cell growth in coal slurries
- 1989
-
Ingår i: Biotechnology Techniques. - 0951-208X. ; 3:5, s. 295-298
-
Tidskriftsartikel (refereegranskat)abstract
- Microbial growth in coal slurries can be detected if surfactant is present in the samples by analysing the protein concentration after disintegration of the cells. Without surfactant present in the samples, the proteins are readily adsorbed on the coal surfaces. A suitable surfactant is sodium dodecyl sulphate at 0.5 to 1% of the sample volume
|
|
| 3. |
- Olsson, G, et al.
(författare)
-
Microorganisms for Desulfurization of Coal: the Influence of Leaching Compounds on their Growth
- 1989
-
Ingår i: Fuel. - 1873-7153. ; 68:10, s. 1270-1274
-
Tidskriftsartikel (refereegranskat)abstract
- An investigation was undertaken to outline how microorganisms suggested for use in coal desulphurization are affected by compounds leached from coal. Three species of the genus Sulfolobus were studied. Sulfolobus acidocaldarius was seen to be affected by compounds leached from coal more negatively than Sulfolobus brierleyi and Sulfolobus solfataricus. It was observed that certain conditions during leaching, such as pH, temperature and leaching time, were important for the concentration of compounds leached from coal. It was seen that compounds leached from coal, in some cases, can improve the growth yield for the microorganisms.
|
|
| 4. |
- Zacchi, Guido, et al.
(författare)
-
Economic evaluation of enzymatic hydrolysis of phenol-pretreated wheat straw
- 1988
-
Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 32:4, s. 460-466
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental data from the enzymatic hydrolysis of phenol-pretreated Swedish wheat straw have been used to evaluate the cost fractions of capital and utility, enzyme, and raw material. Two different raw material prices and varying enzyme prices have been used. The evaluation is based on an empirical model for the enzymatic hydrolysis and a computer program where utility and equipment, enzyme, and raw material prices can be varied. The optimal residence time for the enzymatic hydrolysis is in the range of 70–110 h. A fed-batch procedure with substrate concentrations higher than 10% oven-dried material (ODM) and enzyme concentrations in the range (6–10) · 106 FPU/ton ODM should be used.
|
|
| 5. |
- Ari, E. Aysen, et al.
(författare)
-
Disaggregation under uncertainty in hierarchical production planning
- 1988
-
Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 35:2, s. 182-186
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with a hierarchical planning system that is used for planning of a single-stage manufacturing system. We consider two decision levels, aggregate and detailed planning, and formulate a model for evaluation of aggregate plans and optimal disaggregation in case of independent stochastic demand. It is shown how the optimal solution can be obtained with the aid of a dynamic programming algorithm. Furthermore, we give conditions that will guarantee optimality of a simple intuitive disaggregation rule
|
|
| 6. |
- Axsäter, Sven, et al.
(författare)
-
Combining items for lot sizing in multi-level assembly systems
- 1987
-
Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 25:6, s. 795-807
-
Tidskriftsartikel (refereegranskat)abstract
- Many manufacturing firms are faced with the problem of planning the production/purchase quantities for items in single product, multi-level assembly production/inventory systems. Such systems are characterized by a single product, or end item, used to satisfy customer demand, which is assembled from a number of component items which, in turn, may be assembled from one or more other component items, etc. Component items may be either fabricated or purchased. This paper identifies conditions on the cost parameters which, when applicable, allow items to be combined for purpose of optimization, thereby reducing the size of the problem.
|
|
| 7. |
- Axsäter, Sven
(författare)
-
Control theory concepts in production and inventory control
- 1985
-
Ingår i: International Journal of Systems Science. - : Informa UK Limited. - 0020-7721 .- 1464-5319. ; 16:2, s. 161-169
-
Tidskriftsartikel (refereegranskat)abstract
- The use of efficient production and inventory control systems is of great importance for industry. Therefore this area could be expected to provide many fruitful applications of control theory techniques. However, control theory has traditionally been aimed at applications in other fields, and results have only limited applicability in production and inventory control. This paper gives an overview of earlier research concerning control theory applications in production and inventory control. Areas given special emphasis are those in which control theory seems to have a stronger potential for practical application
|
|
| 8. |
- Axsäter, Sven
(författare)
-
Evaluation of lot-sizing techniques
- 1986
-
Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 24:1, s. 51-57
-
Tidskriftsartikel (refereegranskat)abstract
- Standard lot-sizing models are often not directly applicable in practice. Different assumptions in lot-sizing models and the extent to which these assumptions are valid in various practical situations are discussed. Practitioners also tend to prefer simple standard methods even for complex problems, which means that adjustment of the lot sizes may be desirable. The ways in which such adjustments can be carried out are analyzed.
|
|
| 9. |
- Axsäter, Sven
(författare)
-
Extension of the extended basic period approach for economic lot scheduling problems
- 1987
-
Ingår i: Journal of Optimization Theory and Applications. - 0022-3239 .- 1573-2878. ; 52:No 2, s. 179-189
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problem of choosing cyclical production patterns for several products which are produced on a common production facility. The extended basic period approach of Elmaghraby is extended by allowing more than two basic periods. The problem of dimensionality of the dynamic programming formulation is dealt with by aggregating the capacity data in different basic periods
|
|
| 10. |
- Axsäter, Sven
(författare)
-
Initial order quantities
- 1989
-
Ingår i: Engineering Costs and Production Economics. - 0167-188X .- 1878-4011. ; 15, s. 307-315
-
Tidskriftsartikel (refereegranskat)abstract
- The paper shows how optimal lot sizes are determined in an initial transient phase where the needed lead time may not be available in the production of a batch. It is assumed that the sales are lost. The transient problem is due to the finite production rate. A case is also considered when the constant demand starts suddenly and production is not started in advance. It is assumed that backlogging is not allowed
|
|
