Method for real time measurement of mass flow rate of bulk solids
The mass flow rate of bulk solids in a pneumatic transport system is measured in real time. At least two pressure gauges (P 1 , P 2 ) are provided in a pipe section of the transport system. The pressure drop ΔP between the pressure gauges is determined during a gas-solids flow of air and bulk solids through the pipe section. The suspension density ρ sus of the flowing mixture of air and bulk solids is calculated. The bulk solids mass flow rate M s at a given location along a given length of a pipeline is estimated based at least on the suspension density ρ sus of the flowing mixture.
1. A method for real time measurement of mass flow rate of bulk solids, wherein said bulk solids are loaded, or unloaded, by a pneumatic transport system having a pipe section along which are located at least two spaced-apart pressure gauges (P 1 ,P 2 ), the method comprising:
Determining pressure drop ΔP between said pressure gauges based on information provided by the pressure gauges during gas-solids flow of air and bulk solids through the pipe section,
by a computing device, calculating suspension density ρ sus of the flowing mixture of air and bulk solids based on the pressure drop ΔP, and
by a computing device, estimating the bulk solids mass flow rate M s at a given location along a given length of a pipeline, based at least on the calculated suspension density ρ sus of the flowing mixture,
wherein said suspension density ρ sus of the flowing mixture is calculated using the following formula:
Δ
P
=
1
2
K
ρ
sus
LV
2
D
(
1
)
where K is the coefficient of friction of the bulk solid flowing through the pipeline,
D is the pipe diameter,
L is the length of the pipe section between pressure gauges (P 1 , P 2 ),
V is the local air velocity at the section where the first pressure gauge (P 1 ) is arranged.
2. A method according to claim 1 , wherein said suspension density ρ sus is defined as:
ρ
sus
=
M
s
+
M
air
Q
s
+
Q
air
(
2
)
where M s is the solids mass flow rate,
M air is the air mass flow rate,
Q s is the solids volume flow rate at the section 1 and Q s =M s /ρ s ,
Q air is the air volume flow rate at the section 1;
wherein the mass flow rate of bulk solids is estimated by:
V
s
=
M
s
ρ
s
(
3
)
where ρ s is the solids density.
3. A method according to claim 1 , further comprising calculating cumulative mass flow of solids through a pipe section of the pneumatic transport system based on the mass flow of bulk solids as estimated in real time.
4. A method according to claim 3 , wherein said bulk solids is dry cement or similar material.
5. A method according to claim 1 , further comprising controlling the airflow rate based on the values from the measurements to control the mass flow rate of bulk material.