The paper deals with the impact of co-firing biomass with coal in boilers on the dew point of the flue gas. Co-firing of biomass may have twofold implications on corrosion and fouling, which are the processes that determine the lowest acceptable flue gas outlet temperature and as a result, boiler efficiency. Both phenomena may be reduced by co-firing of usually low sulphur biomasses or enhanced due to increased moisture content of biomass leading to increased water dew point. The present study concerns the problem of low-temperature corrosion in utility boilers. The paper gives (in the form of diagrams and equations) a relationship between water dew point and moisture content of fuel mixture when co-firing coal and various biomasses. The regression analysis shows that despite significant differences in the characteristics of coals and these of additional fuels, which are planned for co-firing in large-scale power boilers, the water dew point can be described by a function given with the accuracy, which shall be satisfactory for engineering purposes. The discussion of the properties of biofuels indicates that the acid dew point surplus over the water dew point (Δtr = tr - twr) is not likely to exceed 10 K when co-firing biomass. The concluding remarks give recommendations for the appropriate operation of boilers in order to reduce risks associated with biomass co-combustion.
In the paper the analysis of random vibration of an actively damped laminated plate with functionally graded piezoelectric actuator layers is presented. The simply supported plate is subjected to stochastic loading represented by a uniformly distributed pressure. The random input is assumed as a Gaussian sta- tionary and ergodic process. The actuators are regarded as a multi-layer structure arranged of piezofiber composite sub-layers. The sub-layers differ each other with amount of PZT (lead-zirconate-titanate) fibers and are stacked to achieve a desired change of the PZT volume fraction through the actuator thickness. The gradation scheme of constituents and material properties are estimated by parabolic and power functions. Numerical simulations are performed to recognize the influence of the applied random excita- tions and the actuator properties gradations on the characteristics of the stochastic field of active plate deflection i.e. power spectral density, autocorrelation function and variance