Jet Sparger Optimisation Heating of water tanks or vessels in many applications is done to stage hot water for use in production, cleaning, line and filter flushing and a number of other uses. Common methods of tank heating are through the use of heat exchangers, eductors or spargers. The incoming water is usually around 45°F – 60°F (7°C – 16°C) and is typically heated anywhere from 100°F – 150°F (38°C – 66°C) for applications involving sanitizing or cleaning.
Tanks and vessel systems typically heated by the use of heat exchangers, eductors, and steam spargers can experience the following issues:
Eliminate Steam Hammer
Spargers and eductors may damage the tank because of the sometimes violent nature of the condensation process
Using an external steam control valve to control steam pressure produces low velocity steam which leads to inefficient steam mixing and condensation. Uncondensed steam will either produce steam hammering or escape to atmosphere leading to energy losses
Heat exchangers require a condensate return system. Plug and ineffective steam traps along with flash releases can lead to energy losses and maintenance issues
Heating of water can leave mineral and scale build-up that causes maintenance and performance problems for heat exchangers and spargers
Some sparger devices use passive springs and tube assemblies that tend to stick, resulting from scale build-up, causing temperature control problems
Jet Diffuser Efficiency
High velocity steam delivery assures complete mixing of steam, reducing occurrences of vibration and saves energy losses from uncondensed steam escaping. Integral stem plug eliminates need for steam pressure control valve.
Single or Multiple Jet Sparger Configurations
A single Jet Sparger can be used for small tanks. When heating larger tanks, or if a higher temperature rise is required, multiple PSX Spargers (2-4) can be placed around the tank. Multiple Jet Sparger configurations also allow for rapid heat-up, and when desired temperature is achieved, (1) PSX Jet Sparger can be operated for trim temperature control.
PSX Heater Solution
Install the PSX Jet Diffuser Tank Mount Sparger on the tank wall to the heat the tank until the tank reaches a steady state temperature. Various size tanks can be accommodated with single or multiple Jet Sparger arrangements.
The PSX heater has a high heating capacity which accelerates tank heat-up time over the time it takes conventional steam sparging. Once the desired tank temperature is achieved, a single the PSX heater steam injector can be operated to allow for trim temperature control of the tank until the desired tank temperature achieved. Injection of high velocity steam minimises improves condensation and mixing, thus structural damage to the tank from the sparger can be eliminated. As the PSX heater utilises sonic velocity steam injection, scale and mineral build issues in the steam injector is eliminated.
The tank temperature can be controlled via a tank sensor, a discharge sensor, a cascade control loop or in a variety of configurations allowing consistent precise temperature control. The internal steam control design of the PSX heater controls the steam mass flow and not the steam pressure, thus eliminating steam hammering and vibration.
Note: Use of tank sparging for applications above 150°F (66°C) may be inefficient and lead to extended heating times. For tank heating applications above 150°F (66°C), the PSX Inline heater is recommended.
Key Direct Steam Injection Benefits
Energy savings resulting from more efficient steam condensation, faster tank heat-up and reduced heat loss to atmosphere
Lower maintenance due to the PSX Jet Spargers self cleaning design
Improved safety due to better steam injection heating methods (elimination of steam hammering)
Better temperature control allows for a more reliable heating process
Reduced maintenance costs from the elimination of condensate return system
Inline process heating has many applications in a variety of process and utility applications. Many industries, such as food, chemical and pulp and paper make use of inline process heating for water, slurry, sludge and aggressive fluid heating applications. Direct steam injection for inline heating is a very good choice for a variety of applications. One of the fundamental principals for efficient and reliable steam injection is the ability to produce and deliver high velocity steam. High velocity steam is what assures rapid and complete condensation and mixing of the steam in the fluid. Often people will look at all forms of steam injection as the same and then make a investment decision based on price.
Internally Modulated vs. Externally Modulated Steam Control
There are two distinct design types of Direct Steam Injection, relative to steam control and they can have a significant impact on the steam injection heater’s performance.
Externally Modulated Steam Control
Externally modulated steam control has been a common approach for direct steam injection heating. This approach uses a Remote Steam Control Valve (PRV) to throttle (reduce) the steam pressure prior to a fixed opening steam injection point. Typically the steam pressure needs to be reduced at least 50% to control the amount of steam for temperature control. As the steam injection point has a fixed opening area, the reduced steam pressure also reduces the velocity (sub-sonic flow) of the injected steam.
Issues
Effective steam condensation rates are dramatically reduced as steam velocity is goes down. When low velocity steam injection occurs, sub sonic steam conditions exist. This results in:
Eliminate Steam Hammer
Low velocity steam leads to uncondensed steam bubbles, which tend to collapse against the pipe walls. This is what leads to the vibration and steam hammering
Uncondensed steam can also travel past the temperature sensor which results in temperature control issues such as over heating
Process upsets are common and damage to equipment can occur from the steam hammer
Maintenance Issues result when steam collapses on the surface or in the steam injector, which leads to excessive wear which increases maintenance costs and reduces reliability
Ultimately problems arise when the steam pressure has dropped to a point where the steam flow is no longer choked and is sub-sonic. This can be seen most often at start-up and shut-down of externally modulated steam injectors in the form of noise, vibration and hammering. With an external steam valve, there is always a pressure drop before the steam reaches the injector. Some sparger devices use passive springs and tube assemblies that tend to stick, resulting from scale build-up, causing temperature control problems. The use of external steam control devices to control the steam flow by modulating the steam pressure can lead to excessive steam hammering and vibration. Steam hammering and vibration often result from poor mixing and condensing of the steam.
As stated above, efficient and reliable condensation of steam is directly dependent on steam velocity. By using a steam pressure reducing valve for control, steam flow will become sub-sonic. The way to overcome this problem is to inject steam at choked flow conditions. Choked flow conditions allow steam to be injected at sonic flow velocities.
ProSonix’s unique method of steam injection utilises an internal steam control to precisely deliver the appropriate mass flow of steam, and not the pressure, for the required heating. This is achieved via and integral pneumatic actuator, and a variable position stem plug in the steam jet diffuser. We do not throttle or regulate steam pressure. This design offers a precise method of steam control through a choked flow control delivery of the steam.
Choked flow is the phenomenon of accelerating a vapor to maximum velocity by creating a pressure differential through an engineered nozzle. By establishing choked flow, the steam mass flow can be metered to precisely control the heating of the liquid. This produces predictable results based on position of the stem plug. Through a variable area steam diffuser, steam flow is metered at the point where steam and liquid first contact and mix. Internally Modulated DSI heating controls the mass flow of the steam and not the pressure.
Key Benefits of Internally Modulated Steam
No process upsets. High velocity steam flow optimizses the steam mixing and condensation with the liquid and eliminates problems with vibration/steam hammering
No steam control valve required asthis method eliminates the need for an external steam control valve or downstream mechanical mixing devices
Rapid and complete condensation of the steam allows for temperature reliable control of +/- 1°F (-17°F).
High velocity steam also is self cleaning and eliminates debris along scale and mineral build-up on the steam diffuser
Lower maintenance costs as proper condensation of the steam eliminates excessive wear
Low pressure drop of typically 1-2 psig reduces pump demand and energy consumption
The PSX inline heater can be controlled either locally or remotely via the plant DCS or PLC control system. Remote control inputs typically used are 3-15 psig, 4-20 mA, or other Fieldbus devices. The PSX heater can be installed on the incoming water or slurry line or in a re-circ heating loop to the tank, re-circulating through the heater until the tank reaches a steady state temperature. The PSX heater has a high heating capacity and can achieve a temperature rise from 1°F to 250°F (-17°C to 121°C) in a single pass through the heater.
It is often desirable to utilise vent or waste steam rather than simply release it to the atmosphere or condense it into water to eliminate the steam. The difficulty has been finding a way to safely and stably condense the steam into a process fluid so the energy can be used in a productive manner. Vent steam is often variable in pressure and availability. Traditional heat exchangers often have trouble functioning in this manner making them problematic.
Some issues associated with heat exchangers
Sizing the exchangers to handle the liquid and steam flow results in the heat exchangers overly large, adding expense and pressure drop to the system
Sizing the trap system for the heat exchanger is difficult to accomplish without the potential of overloading the system with live steam
ProSonix Solution
The ProSonix J-Series Jet Sparger allows the vent steam to be utilised in a safe and simple manner. The flexibility in mounting the heater allows the steam to be condensed in a wide range of pipe sizes, or into a tank or other vessel. Control of the steam addition can be accomplished in a simple manner. Often, a pressure switch is utilised on the vent steam line, activating the PSX heater to quickly condense the steam. An air cylinder on the ProSonix heater quickly opens to allow the steam to disperse quickly and quietly into the flowing fluid. When the steam vent closes, or the pressure drops, the air cylinder on the ProSonix heater closes.
Features & Benefits
It reduces the cost of waste steam that is vented or flashed and sent to drain
Flexible installation as it can be installed inline in the pipe or on a tank or vessel wall
Can be installed directly in the pipe of a tank, thus eliminating the need for floor space or expensive re-working of piping.
Single or multiple unit configurations for tank heating can be installed to allow for large volume heating and then trim heating with a single unit open
More and more agricultural and dairy farms as well as beef, hog and poultry operations are considering the use of anaerobic digestion for biogas production. These operations typically produce a significant amount of organic matter in the form of manure. Anaerobic digestion is a biological process that breaks down organic solids. Manure can be processed in anaerobic digesters and the byproduct is methane gas. The methane gas can be captured, stored and used to run electrical generators and boilers for use in the farm operations. Heat exchangers can face the following challenges when heating sludge:
Live steam used to provide heat for heat exchangers creates hot spots where sludge can burn and build-up plugging the heat exchanger tubes. This increases maintenance costs and an increased pressure drop across the heat exchanger
Upgrading from mesophillic to thermophilic often require multiple heat exchangers in series to achieve the necessary temperature rise
Increased pressure drop adds demand to the sludge pumps thus increasing energy usage
Temperature control problems can be present as there is a lag time from slurry entering and then being discharged
To overcome these challenges, Direct Steam Injection (DSI) is a very good approach. There are correct ways to apply DSI and approaches that may not produce desirable results. One of the key factors to successful DSI is to inject steam at sonic velocity to achieve choked flow.
Spargers, Fixed Eductors &Venturi Style DSI
Eliminate Steam Hammer
These units use a fixed nozzle to inject steam. Steam control is attempted via an externally modulated steam control valve. With an externally modulated steam injecton the steam pressure is adjusted to control the flow rate of steam with a control valve.
Problems arise when the steam pressure has dropped to a point where the steam flow is no longer choked. This can be seen most often at start up and shutdown of externally modulated steam injectors in the form of noise, vibration and hammering. With an external steam valve, there is always a pressure drop before the steam reaches the injector.
The use of external steam control devices to control the steam flow by modulating the steam pressure can lead to excessive steam hammering and vibration. Steam hammering and vibration often result from poor mixing and condensing of the steam. As temperature demand drops, steam pressure drops, lowering the steam velocity and potentially causing instability. Uncondensed steam bubbles will typically collapse when it comes in contact with a cold pipe wall in the liquid piping. When these bubbles collapse, the slurry rushes in to fill the void and impacts the pipe wall. In some cases this will result in some pinging noise and in severe cases, steam hammering and vibration.
PSX DSI Heater Solution
The PSX heater uses a unique method of steam injection via an integral steam control device. The key to efficient, safe and predictable steam injection is to inject steam at sonic velocity to achieve choked flow. All steam injectors need to operate in a choked flow manner for good, non-violent mixing. The PSX heater is an internally modulated injection heater that varies the mass flow rate of steam by changing the area through which the steam may pass. This type of modulation allows the full steam pressure to always be present at the point of injection regardless of the plug position. The PSX heater has an integrated Pneumatic Actuator that allows the engineered steam diffuser opening to vary according to the temperature demand.
Flow rates can range from 1 – 5,000 gpm. The PSX heater has a high heating capacity and can achieve a temperature rise of up to 250°F (121°C) in a single pass through the heater.
Key PSX Heater Direct Steam Injection Benefits
Stable operation due to the internal steam modulation design which controls the steam mass flow and not the steam pressure thus eliminating steam hammering and vibration issues
Low maintenance due to the PSX heater’s self cleaning design
Low pressure drop reduces demand on the sludge pumps lowering energy costs
Better temperature control allows for a more reliable heating process (typically +/- 1%)
Reduced installation and operational costs with the elimination of the condensate return system
Direct mechanical control of the steam injector allows for linear process heating control
Control is maintained by the plant PLC/DCS or local controller with no proprietary software required
PSX heater can be installed in the piping requiring no floor space
Inline process heating with Direct Steam Injection has multiple applications in a variety of process and utility applications. Many applications such as mineral processing, pulp and fiber slurry pre-treatment, oil sands mining and others are not well suited for traditional methods of heating. Typical challenges encountered are corrosive fluids, abrasive particulate, viscosity changes, plugging and fouling, eating for water, slurry, sludge, and aggressive fluid heating applications. Direct Steam Injection for Inline Heating is a very good choice for a variety of applications. One of the fundamental principals for efficient and reliable steam injection is the ability to produce and deliver high velocity steam. High velocity steam is what assures rapid and complete condensation and mixing of the steam in the fluid.
Internally Modulated Steam Control – ProSonix’s unique method of steam injection utilises an internal steam control to precisely deliver the appropriate mass flow of steam, and not the pressure, for the required heating. This is achieved via and integral pneumatic actuator, and a variable position stem plug in the steam jet diffuser. We do not throttle or regulate steam pressure. This design offers a precise method of steam control through a choked flow control delivery of the steam. ‘Choked flow’ is the phenomenon of accelerating a vapor to maximum velocity by creating a pressure differential through an engineered nozzle. By establishing choked flow, the steam mass flow can be metered to precisely control the heating of the liquid. This produces predictable results based on the position of the stem plug. Through a variable area steam diffuser, steam flow is metered at the point where steam and liquid first contact and mix. Internally Modulated DSI heating controls the mass flow of the steam and not the pressure.
Advantages with Multi-Stage DSI Heating
Eliminate Steam Hammer
Eliminate process upsets as some fluids and slurries because of their hi-viscosity/hi-solids are not receptive to large volumes of steam addition. Splitting the heating load can result in improved steam condensation eliminating steam hammering (cavitation) and excessive wear
The PSX inline heater can be designed to match the slurry design flow velocities eliminating flow disruptions, accelerated flow velocity areas and maintaining solids in suspension
Rapid and complete condensation of the steam allows for more reliable temperature control of up to +/- 1°F (-17°C)
High velocity steam is self cleaning and eliminates issues associated with plugging and fouling along with scale and mineral build-up
Lower maintenance costs as proper condensation of the steam eliminates excessive wear, thus improving equipment reliability and life
Typically 1-2 psig reduces slurry pump demand which reduces energy consumption
Oil sands processing in Northern Canada utilizes a variety of solvents and naphtha to assist in the separation of the Bitumen from the water and sand. These fluids can help promote chemical reactions, accelerate processing time, and reduce processing costs. Many of these must recovered due to their high costs, importance of water recovery, or issues associated with release of the chemicals to the environment.
Issues Associated with Oil Sands Processing
The sand that is separated is very abrasive and can cause excessive wear. Devices that accelerate flow or cause impingement will wear very rapidly.
Bitumen and froth are not well suited for heating in traditional heating devices due to issues with pressure drop, abrasion, and plugging/fouling.
Solvents sometimes require high temperatures for processing yet can be very unstable and flash in the pipe if temperatures are not controlled properly.
PSX Heater Solution
Eliminate Steam Hammer
The PSX heater can be installed to heat up the process fluid prior to the flash vessel or recovery tank, and has a high heating capacity and can achieve up to a 250 °F temperature rise in a single pass. For difficult to pump slurries or unstable solvents, the PSX heater can be arranged in a Multi-stage configuration to stage the heating to optimize the process. The key to efficient, safe, and predictable steam injection is to inject steam at sonic velocity to achieve choked flow. By achieving choked flow, sonic velocity conditions can be achieved for steam injection. All steam injectors need to operate in a choked flow manner for good, non-violent mixing. The PSX heater is an internally modulated heater that varies the mass flow rate of steam by changing the area in which the steam may pass. This type of modulation allows the full steam pressure to always be present at the point of injection regardless of plug position. Flow rates can range from 1 – 10,000 gpm.
Key PSX Heater Direct Steam Injection Benefits
Eliminate Process Upsets as the internal steam control design of the PSX heater controls the steam mass flow and not the steam pressure thus eliminating steam hammer and vibration issues.
Lower maintenance due to the PSX heater’s self cleaning design (no scaling or plugging/fouling).
Low pressure drop (typically 1-2 psig) reduce pump integration issues and flow disruptions, and provides energy savings by lowering slurry pump demand.
Improved temperature control (typically +/- 1 °F ) allows for a more reliable heating process.
Improved Reliability as a variety of alloys and wear coatings are available to address wear issues.
