--%>

Dynamic model for the paper machine headbox

Explain and derive the Dynamic model for the paper machine headbox?

E

Expert

Verified

We'll first develop a dynamic model for the paper machine headbox.

A stock balance around the headbox. A suffix hb refers to the head box.

Accumulation = Input – Output

dmhb/dt = ρqin – ρqout

Now ρ, is the stock density, but since the consistancy is 0.5% only,  ρ = ρw = Water density

d(ρVhb)/dt = ρqin – ρqout

dVhb/dt = qin – qout

Ahbdh/dt = qin – qout

where, Ahb, is the c/s area of header and assumed to be constant.

qout, is the flow out of the header, and is only through slice, and can be written as, CAs(2gh)1/2, where As, is the cross sectional area of slice perpendicular to the flow, and C is characteristic constant coefficient for the slice.

Hence,
Ahbdh/dt = qin – CAs(2gh)1/2,

To find, we can write Bernoulli's equation between Vacuum Degasser and Headbox. Suffix vd refers to vacuum degasser.

Pvd/ρ + W = (Phb + ρgh)/ρ + V2/2
 
V = {2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2

qin = AinV =  Ain{2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2

Hence the dynamic model is,

Ahbdh/dt = Ain{2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2 – CAs(2gh)1/2,

where the rate of stock height change in head box is related to the pressure in vacuum degasser and height.

We have to linearize the non linear dynamic model.

So that the effective model will be,

τdh'/dt = KpP'hb  + Khh',

So as we see the the response of the height of stock to variations in vacuum degasser pressure is first order lag. We don't know the dynamics of level sensor or transmitter, but we'll assume it's also first order lag.

Hence the effective system will be a second order. And hence it'll be oscillatory, and we propose the PID controller for level control by manipulating the speed of fan pump.

Using MATLAB control toobox and given values of the parameters in the problem, we approximately find the following controller parameter settings.

    Kc = 9.6, τI = 2.3 min, τD = 3.5 min.

Similarly, a propotional integral controller is proposed for pressure control in head box.

The pressure in the head box is related to in flow of air, which is controlled by PI controller.
The air is available at pressure of 300 kPa.

dPhb/dt = f(Qin), where is the inlet flow rate of air.

This will be pure capacitive system, hence we propose PI controller.

We find the controller parameters for this,

Kc = 14.5, τI = 4.5 min.

   Related Questions in Mechanical Engineering

  • Q : Causes and consequences of dynamic

    Discuss the causes and consequences of dynamic loading on structures based on two real examples. Support your discussion with proper diagrams or sketches. Your discussion shall include the time and location of the event, type and source of dynamic loa

  • Q : Arena simulation Are you able to modify

    Are you able to modify the attached [HW4-4-1sawModifiedInstructorTemplate] with the information below for this assignment? Modify the attached exercise by adding agent breaks. The 16 hours are divided into two 8-hour shifts. Agent

  • Q : Cetane Number and Octane Number

    Describe the term Cetane Number and the Octane Number?

  • Q : Calculating liquid composition There

    There is a 35% MeOH/water mix to feed to a flash at 100 Ib- mole /hr and 1 atm. We want a vapour composition of 60 % MeOH. What does the vapour flow rate need to be? What is the liquid composition? Give the equation of the operation line?

    Q : What is critical speed What is critical

    What is critical speed?

  • Q : Problem on degree of freedom Draw a

    Draw a frequency-response curves for a damped single degree of freedom system subjected to a harmonic excitation under three different damping ratios. System has a natural frequency of ωn as the forcing frequency of the excitation is ω. Describe

  • Q : What is carnot engine Explain the term

    Explain the term Carnot engine?

  • Q : Problem on turbulent flow The

    The approximate equation for the velocity distribution in a rectangular channel with the turbulent flow is 655_turbulent flow.jpg

    Q : Formulating equation of motion Figure

    Figure below shows a reinforced concrete framed building subjected to earthquake ground motion. The floor is rigid with the mass of each floor is shown in the figure. Formulate the equation of motion for this building. Prove that the natural frequenci

  • Q : Convection Heat Transfer Please Solve

    Please Solve this problem Step by step, and the question is in the images.