Short introduction of non mechanical Valves used for solid particulate transfers.

1. NON MECHANICAL
VALVES
P Rahul Palani (1201ME20)
Prit Ranjan (1201ME21)
Raju Gupta (1201ME22)
Ravindra Meena (1201ME23)

2. WHAT IS A NON MECHANICAL VALVE ?
 Non-Mechanical valves are devices that facilitate the flow
of solids between the return leg(stand pipe) and the
furnace without any external mechanical force. Air assists
the movement of solids through these valves.

3. WHY REQUIREMENT ?
 165-Mwe boiler would need to transfer 3600tons/hr of hot solid.
 It is difficult to find inexpensive motorized mechanical device to
transfer stand pipe to furnace(LPC to HPC).
 Also Mechanical Valves are subjected to wear due to high
temperature .
 Without any moving parts, transfers solids from stand pipe to
furnace and don't allow gases to flow furnace to standpipe.
 Known to be heart of CFB(Circulating fluidized bed) plants as
even short interruption will fill cyclone with solids and stop entire
plant.

5. KEY FEATURES
Inexpensive
Robust
Simple in construction
Easy to maintain
No moving parts (Non mechanical
valves)

6. WHERE USED ?
 CFBs (Circulating Fluidized Bed) are widely used in
fossil fuel combustion.
 This is carried out by solid recycle system because
it can transport solids from low pressure (cyclone)
to high pressure region(bottom of the furnace or
riser) and also prevent back flow.

7. WHAT ARE GASIFIERS ?
 Gasification is a process that converts organic or
fossil fuel based carbonaceous materials into
carbon monoxide, hydrogen and carbon dioxide.
 This is achieved by reacting the material at high
temperatures (>700 °C), without combustion, with a
controlled amount of oxygen and/or steam. The
resulting gas mixture is called syngas (from
synthesis gas or synthetic gas) or producer gas and
is itself a fuel

8. Types of Non-Mechanical valves :-
There are many types of Non-Mechanical valves.
Examples :
1. L-Valve
2. J-Valve
3. V-Valve
4. Reverse Seal Valve
5. Loop Seal
6. Seal Pot
Work Best with particles size >150μm.

9. Flow through these valves can be stopped by shutting of the supply of aeration gas.

10. V- VALVE
 The V-valve is a special purpose
valve available for CFB reactors,
is not normally used in CFB
boilers or gasifiers.
 The V-valve provides very good
protection against gas leakage
between the furnace and the
return leg, even if it operates with
a large pressure difference.
 It can operate over large range of
flow rates as compared to L and
J valves.

11.  It consists of a V-shape channel and a standpipe
both connected through a aperture.

12. Analogy To Principal Operation
The principle of working a non-mechanical valve can be
explained by the example of moving water in a loop by
aeration

13.  Under Normal Conditions water will remain
stationary and static pressures at B and C will be
equal.
 Injection of lighter air bubbles will reduce the bulk
density in column CD as a result static pressure of
C will decrease and there will be continuous
circulation of water.
 This analogy can be applied directly to gas-solid
system in CFB provided the solids in the standpipe
behave as a liquid , meaning they deform
continuously under the action of shear stress.

14. STANDPIPE
 Vertical of inclined tube in which granular solids
flow downwards.
Functions :
 Transfer solids to high pressure from low pressure.
 Provide seal against gas flow in one direction.

15. L-VALVE
CFB Plant with L-Valve

16.  L-Valve is generally used in CFB.
 consists of a right-angled, L-shaped pipe
connecting the two vessels between which the
solids are to be transferred
 In a CFB boiler, vertical leg of the L-valve is
connected to the solid hopper of the cyclone(or any
gas-solid separator). The horizontal section of the
L-valve is connected to the CFB furnace.
 The L-valve would usually have a moving packed
bed in the standpipe and a less dense bed in the
furnace into which solid is fed

17.  A small amount of air or gas is injected into the
vertical leg of the L-valve.
 This air/gas lubricates the packed solids to facilitate
their movement from the dense vertical leg to the
relatively dilute bed. In large commercial units this
air may have to be added in multiple points to
facilitate smooth solid flow.
 The aeration air moves downward through the
particles and then through the constricting bend of
the L-valve.

18.  Solid flow commences only beyond a certain
minimum value of air rate.

19. DESIGN OF L-VALVE
 Design methods of L-valve can be developed from
a pressure balance across the CFB loop.
 Pressure drop across the standpipe must be
balanced by the pressure drop across rest of the
CFB loop.

21. Pressure drop through standpipe
= Pressure drop through(L-valve bend+ Horizontal
arm of L-valve + Furnace + Cyclone )

22.  Maximum Pressure drop in the standpipe
=
This happens when standpipe is at minimum
fluidization.
Lmin= minimum height of solids in the standpipe
The height of solids in vertical column is generally 1.5
to 2 times of this Lmin

23.  Solids in the standpipe are in a moving packed-bed
condition. So the pressure drop through the
standpipe will rise if the relative velocity between
the solids and the gas is increased. The pressure
drop will rise until it is equal to the weight of solids
in the standpipe, that is, when a minimum fluidizing
condition in the standpipe is reached.

24. Loop Seal

25. FUNCTIONING:
 The basic function of loop seal is to give fluid properties
to solid when subjected to static pressure difference by
giving appropriate amount of air.
 Divided in two chamber:
1. Supply Chamber 2. Recycle chamber
 For proper function air is added which reduce inter-particle
force and allows flow under gravitational force.
 Recycle chamber is kept in fluidized state by feeding air
from bottom.
 Flow of solid depends upon ratio of slit height and slit
length both, flow rate etc.

26. DESIGNING OF LOOP SEAL
 Sizing of loop seal is important as small size may
not allow adequate flow of solid and too large will
require large volume of air.
 Standpipe inner diameter(d) can be approximated
by required pressure drop across standpipe and
similar for recycle chamber.
 Length of loop seal, L=2.5 x d, and width of loop
seal 1.25 x d .
 Height of opening is given by as follows in terms of
flow density, velocity, friction, solid flow rate ...

27. FLOW IN WEIR:
 Weir is wall in recycle chamber with lowest height
which controls the flow rate.
 Basu and Botsio (2005) found empirical relation
relating flow rate through the loop seal Ws.
 C is in range of 0.065 to 0.08 for 150 o 250 micro
meter particle. W and H are width and height of
weir.

28. Practical considerations
Problems
 Plugging of loop Seal
-Bed solids are too
flaky to move.
-Boiler burn fuel that
make solids sticky.
 Pressure Surge
-Increase in solid
circulation which cause
pressure surge.
Solution
 Mechanical Means
(Wider, Large, More
smooth flow of solids)
 Increased aeration
 Chemical
Compositions (Which
avoid less
agglomeration)

29. BIBLIOGRAPHY
•Power Plant Engineering by PK NAG
•Chong et. al. 1988 Non-Mechanical
Valves.
•P Basu, S.A Frazer Circulating Fluid Bed
Boilers.