environmental engineering dr jawad al-rifai

Environmental EngineeringDr Jawad Al-rifai

Lecture no. Reactor

Philadelphia UniversityFaculty of Engineering

Department of Civil Engineering

Definition:

• The tanks in which physical, chemical and biochemical. Ex Water softening & Wastewater treatment

Reactor Types1- Batch reactor

• Fill & draw types; materials are added to the tank, mixed for sufficient time to allow reaction to occur and then drained. Ex. Laboratory experiment. – Size < 150m3/d– Inexpensive– Easy to operate & build – No influent or effluent –step increase or pulse;

Mass balance Ct/Co=e-kt

Co: concentration at time zeroCt: concentration at time tK: rate of reactionT: time

Continuous flow stirred tank reactor (CSTR)(Completely mixed flow reactor (CMFR))

• Material flows into, through and out of the reactor at all times• uniform throughout the tank• Ex rapid mix or flash mix tank for Water treatment, wastewater

treatment• Ex natural system; lake, mixing of two streams, air in the room• Water flow > 150m3/d• The composition of the effluent is the same as the composition in the

tank• Mass balance express as

Qin = Qout at no reaction

Ct=Co exp (-t/to)

Plug flow reactors (PFR)• Fluid particles pass through the tank in sequence. • Those that inter first leave first. • Assuming no mixing occur in the lateral direction.• As long as the flow conditions remain steady, the

composition of the effluent remains constant.• Ex. Pipes, long narrow rivers, biological treatment in WWTp• MB eq:

In (Cout/Cin)=-K L/U= -k V/QL: length of plug-flow segmentu: Linear velocity, m/s