Abstract: An apparatus to be applicable as a boiler for incinerating wet refuse in a combustion chamber with a fluid and heat medium of solid particles fluidized by an air feed to form a fluidized bed, with the aid of combustion of auxiliary fuel effected below the fluidized bed, is provided with additional one or more adjacent upper fluidized fed chambers in series to have the wet refuse dried and partially incinerated in the lower primary fluidized bed chamber with the balance of the refuse in a form of unburnt carbon particles being forced to fly upward into the additional upper fluidized bed chambers and be incinerated therein. Heat recovery is carried out from a topmost fluidized bed chamber.

Abstract: A high pressure evaporation vessel which is operated at a predeterminate pressure above atmospheric pressure, is connected to a low pressure expansion vessel which is operated at a predeterminate pressure below the pressure prevailing in the high pressure evaporation vessel, through a U-shaped siphon tube. The U-shaped siphon tube contains a liquid column absorbing the pressure difference existing between the high pressure evaporation vessel and the low pressure expansion vessel.

Abstract: A solid fuel obtained by mixing highly combustible, fusible materials such as polymer resin, and low calory powder such as fuel combustion ashes containing unburnt carbon components and inorganic component, and molding the mixture. The solid fuel has a controlled calorific value and a controlled combustion rate with a good shape retention.

Abstract: A caustic alkali solution is concentrated to high density or high caustic alkali concentration by evaporation under high pressure at elevated temperature and expansion of the thus obtained concentrated caustic alkali solution to low pressure, preferably below atmospheric pressure. The pressure difference between the high pressure evaporator and the low pressure expansion vessel is absorbed gradually by a pressure difference absorber, preferably comprising a liquid column in a U-shaped siphon tube, so that corrosion and erosion are reduced considerably.