Wednesday, October 31, 2018

Understanding Pressure-based Flowmeters

A “plug” of fluid can be accelerated by applying a difference of pressure across its length. The amount of pressure applied will be in direct proportion to the density of the fluid and its rate of acceleration. Conversely, we may measure a fluid’s rate of acceleration by measuring the pressure developed across a distance over which it accelerates.

We may easily force a fluid to accelerate by altering its natural flow path. The difference of pressure generated by this acceleration will indirectly indicate the rate of acceleration. Since the acceleration we see from a change in flow path is a direct function of how fast the fluid was originally moving, the acceleration (and therefore the pressure drop) indirectly indicates fluid flow rate.

A very common way to cause linear acceleration in a moving fluid is to pass the fluid through a constriction in the pipe, thereby increasing its velocity (remember that the definition of acceleration is a change in velocity). The following illustrations show several devices used to linearly accelerate moving fluids when placed in pipes, with differential pressure transmitters connected to measure the pressure drop resulting from this acceleration:

Pressure-based Flowmeters

Another way we may accelerate a fluid is to force it to turn a corner through a pipefitting called an elbow. This will generate radial acceleration, causing a pressure difference between the outside and inside of the elbow which may be measured by a differential pressure transmitter:

Pressure-based Flowmeters

The pressure tap located on the outside of the elbow’s turn registers a greater pressure than the tap located on the inside of the elbow’s turn, due to the inertial force of the fluid’s mass being “flung” to the outside of the turn as it rounds the corner.

Yet another way to cause a change in fluid velocity is to force it to decelerate by bringing a portion of it to a full stop. The pressure generated by this deceleration (called the stagnation pressure) tells us how fast it was originally flowing. A few devices working on this principle are shown here:

Pressure-based Flowmeters



Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

Monday, October 29, 2018

Reboiler Condensate Level Measurement Using a Non–intrusive Magnetostrictive Level Transmitter

Magnetostrictive Level TransmitterIntroduction

Reboilers are found throughout refineries and are critical to reliable plant operation. Reboilers are designed to operate with no liquid condensate level. Unintentional condensate flooding of reboilers results in a greater risk of corrosion since corrosion processes occur in the liquid phase. Uncontrolled corrosion can lead to reboiler failure and unplanned shutdown costing billions of dollars.

The Application

The customer is a fractionation plant which produces ethane and propane. The application, reboiler condensate level, is critical to the plant operations. Process conditions: The transmitter is mounted as a non–intrusive device, so pressures are of no consequence.
  • Ambient temperature: –2 to 43 deg. C (28.4 to 109.4deg. F)
  • Process temperature: 65 deg. C (149 deg. F) 
  • Process pressure: 22 barG
The Challenge

The condensate–pot level indicator was unreliable and insensitive to the variations in level–control– valve opening. Condensate–pot level control was poor, and the control valve had to be operated on manual. Finally this competitor transmitter failed and was replaced by the earlier generation magnetostrictive AT200 transmitter years ago. The customer is now looking to upgrade the measurement system.

The Solution

ABB offered the advanced next generation LMT series magnetostrictive transmitter for the level measurement. The LMT200 initially was added as a redundant measurement for ensuring the performance and reliability. The customer appreciated the advanced features including the Easy setup, built–in waveform and diagnostics capabilities of the LMT. This resulted in a higher confidence and switched the LMT measurement loop as the primary for the level control through the control system.

For more information contact Hile Controls of Alabama by visiting https://hilealabama.com or by calling 800-536-0269.

Reprinted with permission from ABB Measurement & Analytics.

Monday, October 22, 2018

Your Choice for Process Control Instrumentation - Hile Controls of Alabama


When you need pressure, temperature, level, flow, gas detection or analytical instrumentation, think Hile Controls of Alabama.  Hile provides process instrumentation for the oil and gas, chemical, power, plastics, mining, water and waste water, pharmaceutical and bio-pharmaceutical, food and beverage, pulp and paper, and government-related industries. Located in Pelham, Alabama, Hile Controls of Alabama proudly serves the states of Alabama and Mississippi, as well as Western Tennessee and the Florida Panhandle.

https://hilealabama.com
800-536-0269

Sunday, September 30, 2018

Pulp and Paper Mills: Thermal Flow Meter Opportunities

Reprinted with permission from Kurz Instruments
Thermal Flow Meters for Dry & Wet Gas Applications
Kurz Thermal Flow Meters
for Dry & Wet Gas Applications
There are an estimated 700 pulp and paper manufacturing facilities throughout the U.S.  Trees used in paper making are put through a debarker and a chipper, where they are reduced to approximately one-inch wood chips. The wood chips are pressure cooked in a digester and become pulp, which is refined, turned into slush, and screened. Screening drains away liquid, and the resulting pulp is pressed into paper.

Several steps within the pulp and paper making process create emissions that must be monitored and reported:
  • Bark is typically burned as fuel for a boiler.
  • Chemicals (green liquor and white liquor) used in the digester to separate the cellulose fibers that become pulp result in emissions containing formaldehyde, methanol, acetaldehyde, and methyl ethyl ketone.
  • High temperatures during the washing and screening processes generate exhaust gases.
  • Any bleaching process includes chlorine or peroxide that must be vented.
  • Fiber particles and chemicals are filtered out and recovered. The recovered material is called “black liquor” and is burned in a recovery boiler to provide additional power for the mill, generating exhaust gases.
  • Wastewater generated during the pulp process is diverted to a wastewater treatment facility, where it is treated and recycled before being reused or released. 
Creating paper pulp relies on a careful balance of low velocity air flows among the various processes. For example, the recovery boiler following the digester must be modulated to follow changes in the digester load. Other imbalances can:
  • Create excessive amounts of pollutant gases 
  • Create extra soot to coat boiler tubes
  • Reduce chemical recovery efficiency 
  • Cause excess corrosion problems for boiler components
  • Reduce the boiler’s steam production
Simplified Recovery Boiler
Simplified Recovery Boiler (click for larger view)
A recovery boiler uses the chemical reaction of the black liquor to generate heat for the boiler. It has three air flow systems that must be accurately controlled to create stable air flows:

  • The primary air flow system maximizes chemical recovery. Primary air optimizes bed size, shape, and temperature.
  • A secondary air flow system is used to maintain complete combustion with dynamic mixing. The secondary air dehydrates the black liquor, and controls bed size, shape, and height.
  • A tertiary air flow system is used to prevent the chemical reaction/processes from reaching the upper regions of the boiler and damaging the boiler tubes. This also generates an even temperature profile across the unit.
  • The molten waste is recovered and dissolved in water to create the green liquor used in the separation process.


THERMAL FLOW METER APPLICATION OPPORTUNITIES


Specific installations have included flow meters used in the following environments:
  • Measuring combustion air to a boiler
  • Measuring primary/secondary/tertiary air to a recovery boiler
  • Monitoring stack flue gas
  • Measuring stack emissions
  • Monitoring digester gases and aeration air
  • Measuring inlet combustion air to gas turbine generator sets 
  • Controlling tight fuel-to-air tolerances, such as with natural gas
  • Measuring turbine exhaust gases
  • Measuring overfire and underfire air
For more information on Kurz Thermal Flow Meters, contact Hile Controls of Alabama by visiting https://hilealabama.com or by calling 800-536-0269.

Wednesday, September 26, 2018

Digital Mass Flow Meters and Controllers for Gases - Principle of Operation

MASS-STREAM Digital Direct Mass Flow Meters and Controllers
Digital Mass Flow Meter and
Controller (Bronkhorst)
Principle Of Through-Flow Measurement

The mass flow meters and controllers consist of a metal body with a straight-through flow path. Two sensors are encased with stainless steel and protrude inside this bore; one is designed as a heater and the other one is designed as a temperature probe. A constant difference in temperature (ΔT) is created between the two sensors. The heater energy required to maintain this ΔT is dependent on the mass flow. The working principle is based on King’s law of the ratio between the mass flow and the heater energy. That means the higher the flow, the more energy is required to maintain the chosen ΔT.

Watch this video for an excellent visual understanding.


Applications:
  • Measurement and control technology
  • Aeration
  • Analytical instruments
  • Biogas applications
  • Burner controls
  • Coating plants
  • Exhaust gas measurement
  • Gas consumption measurement
  • Gas monitoring systems
  • Gas purging
  • Mechanical engineering
  • N2/O2-generators
  • Paint-spray lines
800-536-0269



Tuesday, September 18, 2018

Multi-Wavelength Pyrometers

Multi-wavelength pyrometer
Multi-wavelength pyrometer (Williamson)
Some materials can be difficult or near impossible to measure with precision using single-wavelength or ratio pyrometers because of their complex emissivity characteristics. These types of materials are called non-greybody materials and their emissivity varies with wavelength.

Multi-wavelength pyrometers use application specific algorithms to characterize infrared energy and emissivity across the measured wavelengths to accurately calculate both the actual temperature and emissivity of these complex non-greybody materials.

MW pyrometers are best for non-greybody materials as they are able to accurately correct for emissivity variations due to:
  • Changes in alloy, surface texture, surface oxidation
  • Abnormal operating conditions such as a furnace leak, bad roll, or reheated coil (Annealing Line)
For more information about multi-wavelength pyrometers, review the embedded document below, or download a PDF version of "Multi-Wavelength Pyrometers" here.

For application assistance, contact Hile Controls of Alabama by visiting https://hilealabama.com or by calling 800-536-0269.