Fluidized-bed reactor and a temperature-controlling method for the fluidized-bed reactor

A temperature-controlling method for a fluidized-bed reactor for conducting an exothermic gas phase reaction for obtaining malic anhydride from butane in the fluidized-bed reactor, the fluidized-bed reactor having a plurality of heat-removing pipes disposed in the fluidized-bed, the method comprising:

• supplying a first coolant at a stationary velocity to at least one of the heat removing pipes,
• simultaneously supplying a second coolant at a variable velocity to at least one of the other heat-removing pipes, the second coolant being a gas,
• removing not less than 50% of the total amount of heat to be removed utilizing the latent heat of vaporization of the first coolant,
• feeding the second coolant at the variable velocity depending on a temperature detected by a temperature detection section in the fluidized-bed,
• providing a catalyst having a weight-average particle diameter of from 30 to 100 .mu.m, containing 20 to 70% by weight of a fine powder with a particle diameter of not more than 44 .mu.m and having a particle density of not more than 3000 kg/m.sup.3, and
• fluidizing the catalyst by introducing a gas from a lower portion of the fluidized-bed reactor.