Autonomous frequency regulation by controllable loads to increase acceptable wind power generation

Output power fluctuation of high penetration of wind power causes demand and supply imbalance in electric power systems and results in frequency deviation if the fluctuation is not fully compensated by other regulable power plants. In Japan, some electric utilities have started to accept only the wind farms which disconnect and give up generating power during light‐load periods with less adjustable reserve. Otherwise, wind farms are required to employ battery energy storage systems (BESSs) to charge the generated power during the light‐load periods. Instead of these uneconomical solutions, this paper proposes autonomous frequency regulation by controllable loads such as electric water heaters (EWHs). In the paper, the acceptable increase of wind power generation by the proposed load control has been evaluated quantitatively in the power system of the Hokkaido Island in Japan. The result indicates that the acceptable increase of wind power generation goes from 250 to 675 MW by applying the proposed autonomous frequency regulation on all EWHs, and the total cost to implement the autonomous frequency regulation on the EWHs is around 1/26 compared with a solution using BESSs. Copyright © 2009 John Wiley & Sons, Ltd.     

Improved yields of cyclic nigerosylnigerose from starch by pretreatment with a thermostable branching enzyme

Cyclic nigerosylnigerose (CNN) is produced enzymatically from starch by the combined action of 6-α-glucosyltransferase and 3-α-isomaltosyltransferase. In our previous study, α-1,6-branching chains found in the structure of amylopectin and glycogen were shown to be favorable for CNN formation by the two enzymes. Therefore, we examined whether the introduction of α-1,6-branch points into starch using the action of branching enzyme (BE) could improve the yield of CNN from starch. Thermostable BE from Geobacillus stearothermophilus TC-91 was prepared as a purified recombinant protein. Pretreatment of amylose with BE considerably increased the CNN yield from 5% to 38%. When BE acted on tapioca starch, the CNN yield was elevated from 47% to 60%. Conversely, BE treatment of waxy corn starch containing very little amylose resulted in a negligible increase in CNN yield. In addition, BE exerted a beneficial effect when starch with a lower degree of hydrolysis was used as a substrate. The present results indicate that the addition of α-1,6-glucosidic linkages to starch using BE is an effective strategy to improve the yield of CNN from starch.     

Effects of some anionic polysaccharides on the gelatinization and retrogradation behaviors of wheat starch: Soybean-soluble polysaccharide and gum arabic

Gelatinization and retrogradation behaviors of wheat starch were investigated in an aqueous system in the presence or absence of some anionic polysaccharides, soybean-soluble polysaccharide (SSPS), and gum arabic (GA). Weight-average molecular weight was almost equivalent between SSPS and GA, while z-average root-mean-square radius of gyration of GA was ca. twice as large as that of SSPS. The addition of each polysaccharide (0.1–1 w/v%) decreased the peak viscosity of the composite system (starch concentration: 5% or 13%) during gelatinization, and this effect of SSPS was greater than that of GA at the higher starch concentration. It also shifted the onset of viscosity increase to lower temperatures at the higher starch concentration, but no difference was seen in this effect between SSPS and GA. The addition of each polysaccharide (0.1–1%) decreased the amount of amylose leached during gelatinization, and this effect of SSPS was generally greater than that of GA. It hardly altered, on the other hand, the average particle diameter of the starch granules after gelatinization. “Starch ghosts” were less frequently observed microscopically in the presence of each polysaccharide, which appeared to exist around the surface of the starch granules to inhibit amylose leaching. The addition of each polysaccharide (0.5%) increased the rate constants, representing short-term (24 h) retrogradation of starch (5%). It also decreased the saturated dynamic storage modulus of the composite system after storage at 4 °C for 24 h, and this effect of SSPS was greater than that of GA with larger amount of syneresis generated. The results were discussed mainly in relation to the phase arrangement between starch components and each polysaccharide.