Differential Pressure Level Gauge is an instrument that calculates the liquid level (differential pressure) of an object in a vessel by measuring the pressure difference at two different points of the vessel.
Technical Principles
Conventional differential pressure transmitters perform level measurement by measuring the level pressure in a vessel.For example, a 500 mm water column corresponds to a pressure of 500 mmH2O.However, in many applications there is additional vapor pressure above the liquid.Since vapor pressure is not part of the level measurement, pilot tubes and capillary tubes with seals are required to counteract its presence.
Capillary columns and sealing systems solve many of the installation problems of pilot tubes.These systems consist of an external sensing diaphragm connected to the differential pressure transmitter via an oil-filled capillary tube column.Changes in pressure cause displacement of the diaphragm so that the pressure is transmitted to the transmitter through the oil-filled capillary.The oil-filled capillary system is carefully welded and fabricated so that it is a reliable sealing system.This type of construction eliminates leak points and blockages that can develop in the pilot tube.
Electronic remote sensing technology
ERS Electronic Remote Sensing technology solves the common problem of level measurement on tall vessels and towers.The ERS Electronic Remote Sensing system utilizes two directly mounted 3051S pressure transmitters instead of a single differential pressure transmitter using a capillary tube.The two pressure transmitters measure the pressure values on the high and low pressure sides and calculate the differential pressure from the master gauge in both pressure transmitters; this is transmitted back to the host system or DCS system using a standard two-wire 4-20 mA HART signal.In addition to measuring the differential pressure, the pressure values of the high and low pressure sides can be output at the same time, and the differential pressure can also be directly converted into a level value for output and display.
The unique digital architecture of the ERS Electronic Remote Transmission System provides many benefits when used on tall vessels and towers:
Improved Performance
The ERS system utilizes a digital architecture instead of mechanical components for faster response times and a more stable and repeatable measurement, even over wide temperature ranges.Measurement accuracy can be improved by a factor of ten or more.
Simplified Installation and Maintenance
Cold weather installations often require heat tracing or insulation.Pilot tubes need to be inspected for leaks, condensation, evaporation, and clogging, and the digital architecture of the ERS system eliminates these practices, resulting in cleaner installations with less maintenance and upkeep.
Additional Process Data and Diagnostics
The ERS system is a multi-parameter system that provides additional process optimization control information.In addition to level counting, ERS provides real-time access to readings from each pressure sensor and proportional outputs from level or volume measurements.
Shortcomings of conventional differential pressure level technology
Although a proven and reliable technology, double flange differential pressure level systems have been difficult to use in tall vessels and towers.These require longer capillary tubes for ease of installation, and long capillary tube distances make the transmission of pressure inaccurate and more pronounced when the ambient temperature varies.At the same time, the installation process is more demanding and the pilot tube may be unreliable, which is a very serious problem.
Digital Differential Pressure Level Meter
On the basis of the traditional differential pressure level meter, the trend towards digitization has become more and more pronounced in recent years.
Typical application
The main applications are differential pressure or level measurement in distillation columns, chemical storage tanks, sulfate slurry vessels, enzyme fermentation, alkylation reactions, beer fermentation, etc.
1, in the oil pipeline filter differential pressure monitoring applications
Requirements: Oil and gas pipelines need to have filters at certain intervals to filter the transported media to ensure the quality of the transported media and the safety of the pipeline.The differential pressure on both sides of the filter directly reflects the working condition of the filter, if the differential pressure is greater than the design value, then it is likely that the filter is clogged and needs to be repaired and maintained.Traditional differential pressure measurement is the use of differential pressure transmitter and capillary tube composed of DP measurement system, there are installation complexity, affected by the ambient temperature, the problem of poor accuracy.And need to install a separate pressure transmitter to monitor the static pressure of the pipeline.
Solution: Use ERS electronic remote transmission installed on both sides of the filter, spanning about 6 meters; medium temperature within 50 degrees Celsius.The static pressure of the pipeline is about 1.5mPa, the filter design differential pressure is 50kPa, the static pressure: differential pressure is less than 30:1, the calculated accuracy results in 3% or less.
The use of ERS electronic remote transmission, eliminating the capillary insulation accompanied by heat, eliminating the need to install a separate pressure transmitter (ERS can be output pipeline static pressure), and maintenance costs are reduced; response time is faster, changes in ambient temperature does not affect the results of the measurement; the installation has become more convenient.
2、Application of desulfurization gypsum liquid density measurement in thermal power plant
Requirements: Most of the power plant desulfurization uses limestone gypsum wet desulfurization technology, which utilizes gypsum liquid as an absorbent to absorb SO2 and reduce pollution to the environment.The efficiency of desulfurization is generally measured by measuring the density of gypsum liquid.Ordinary gypsum liquid density measurement is to use density meter or mass flow meter to directly measure the density, there are high cost, easy to be damaged, subject to the environmental impact of the problem of large
Solution: Use ERS electronic telemetry mounted in a fixed position and back calculate the average density from the differential pressure between this fixed position, ρ=DP/g*h.
The ERS electronic telemetry installed in the measurement tank of the high and low pressure measurement, through the differential pressure to calculate the density; or directly to the ERS electronic telemetry installed in the desulfurization absorber tower, the upper and lower flange spacing is fixed for 4 meters, because the absorber tower level can be guaranteed in the 10 meters above the low-pressure side of the completely, so this density can be used as the average density of gypsum liquid value.
This program eliminates the mass flowmeter or density meter, investment is reduced, and the original mass flowmeter in gypsum liquid measurement is fragile, the use of ERS can make the one-time investment and maintenance costs reduced by more than 70%; accuracy is improved; the response time of the ambient temperature changes do not have an impact on the measurement results; installation has become more convenient.
3、Application in storage tank level measurement
Requirement: Differential pressure level measurement with large flange spacing.Level measurement of a raw material storage tank with a flange spacing of 16 meters.With the traditional double flange form of liquid level measurement accuracy is very poor; response time is long; day and night, winter and summer measurement results are very different; maintenance costs are high.
Solution: The customer has two identical raw material storage tanks, one of which uses a traditional double-flange differential pressure level meter, and the other uses ERS electronic telemetry after the technical modification, with the original flange interface retained for the process connection, and no change in the tank body.
After using ERS electronic telemetry, the accuracy is changed from 5% of the original program to 0.5%, which is a 10-fold improvement; the response time is shortened from 3 seconds to 0.5 seconds, which is a 6-fold improvement; changes in the ambient temperature do not have an effect on the measurement results; and the installation and maintenance become more convenient.
