Boiler Systems and HVAC: Operation and Efficiency

Posted on Mar 6, 2025 in Technology

Boilers

A boiler is an enclosed vessel that provides a means for combustion heat to be transferred into water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and cheap medium for transferring heat to a process.

When water is boiled into steam, its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be extremely dangerous equipment that must be treated with utmost care. The water supplied to the boiler that is converted into steam is called feed water.

The two sources of feed water are:

  • Condensate or condensed steam returned from the processes
  • Makeup water (treated raw water) which must come from outside the boiler room and plant processes

For higher boiler efficiencies, the feed water is preheated by an economizer, using the waste heat in the flue gas.

Typical Boiler Specification

  • Boiler Make & Year: XYZ & 2003
  • MCR (Maximum Continuous Rating): 10TPH (F & A 100°C)
  • Rated Working Pressure: 10.54 kg/cm2(g)
  • Type of Boiler: 3 Pass Fire tube
  • Fuel Fired: Fuel Oil

Selection of Boiler

  • The working pressure & quality of steam
  • Steam generation
  • Floor area available
  • Accessibility for repair & inspection
  • Comparative initial cost
  • The fuel & water available
  • Operating & maintenance cost

Boiler Properties

  • Safety
  • Accessibility
  • Capacity
  • Efficiency
  • Simple in construction
  • Initial cost and maintenance cost
  • Capable of quick starting and loading
  • Generate maximum steam
  • Weight and space
  • Cost

Boiler Types and Classifications

Horizontal, Vertical, or Inclined:

  • If the axis of the boiler is horizontal, the boiler is called horizontal.
  • If the axis is vertical, then it is called vertical.
  • If the axis is inclined, then it is called inclined.

Advantage of Horizontal Boiler

  1. It can be easily repaired.
  2. It occupies less floor area.

Fire Tube or “Fire in Tube” Boilers

Fire tube boilers contain long steel tubes through which the hot gasses from a furnace pass and around which the water to be converted to steam circulates. Fire tube boilers typically have a lower initial cost, are more fuel-efficient, and easier to operate, but they are limited generally to capacities of 25 tons/hr and pressures of 17.5 kg/cm2.

Water Tube or “Water in Tube” Boilers

In water tube boilers, the conditions are reversed with the water passing through the tubes and the hot gasses passing outside the tubes. These boilers can be of single- or multiple-drum type. These boilers can be built to any steam capacities and pressures and have higher efficiencies than fire tube boilers.

Packaged Boiler

The packaged boiler is so-called because it comes as a complete package. Once delivered to the site, it requires only the steam, water pipe work, fuel supply, and electrical connections to be made for it to become operational. Package boilers are generally of shell type with fire tube design so as to achieve high heat transfer rates by both radiation and convection.

Chain-Grate or Traveling-Grate Stoker Boiler

Coal is fed onto one end of a moving steel chain grate. As the grate moves along the length of the furnace, the coal burns before dropping off at the end as ash. Some degree of skill is required, particularly when setting up the grate, air dampers, and baffles, to ensure clean combustion leaving a minimum of unburnt carbon in the ash.

Spreader Stoker Boiler

Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fast-burning coal bed. This method of firing provides good flexibility to meet load fluctuations since ignition is almost instantaneous when the firing rate is increased.

Pulverized Fuel Boiler

Most coal-fired power station boilers use pulverized coal, and many of the larger industrial water-tube boilers also use this pulverized fuel. This technology is well-developed, and there are thousands of units around the world, accounting for well over 90% of coal-fired capacity. The coal is ground (pulverized) to a fine powder so that less than 2% is +300 micrometers (μm) and 70-75% is below 75 microns, for bituminous coal.

FBC Boiler

When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream.

Performance Evaluation of Boilers

The performance parameters of a boiler, like efficiency and evaporation ratio, reduce with time due to poor combustion, heat transfer surface fouling, and poor operation and maintenance. Even for a new boiler, reasons such as deteriorating fuel quality, water quality, etc. can result in poor boiler performance.

Boiler Efficiency

Thermal efficiency of a boiler is defined as the percentage of heat input that is effectively utilized to generate steam.

  1. The Direct Method: Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel. This is also known as the ‘input-output method’ due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency.

    Efficiency = (Heat Output / Heat Input) x 100

Advantages of Direct Method

  • Plant personnel can quickly evaluate the efficiency of boilers.
  • Requires few parameters for computation.
  • Needs few instruments for monitoring.

Disadvantages of Direct Method

  • Does not give clues to the operator as to why the efficiency of the system is lower.
  • Does not calculate various losses accountable for various efficiency levels.
  1. The Indirect Method: Where the efficiency is the difference between the losses and the energy input. The indirect method is also called the heat loss method.

The efficiency can be arrived at by subtracting the heat loss fractions from 100. The standards do not include blowdown loss in the efficiency determination process.

Boiler Blowdown

When water is boiled and steam is generated, any dissolved solids contained in the water remain in the boiler. If more solids are put in with the feed water, they will concentrate and may eventually reach a level where their solubility in the water is exceeded and they deposit from the solution. Above a certain level of concentration, these solids encourage foaming and cause carryover of water into the steam. The deposits also lead to scale formation inside the boiler, resulting in localized overheating and finally causing boiler tube failure. Blowdown is necessary to protect the surfaces of the heat exchanger in the boiler.

Conventional methods for blowing down the boiler depend on two kinds of blowdown – intermittent and continuous.

Intermittent Blowdown

Intermittent blowdown is given by manually operating a valve fitted to a discharge pipe at the lowest point of the boiler shell to reduce parameters (TDS or conductivity, pH, Silica, and Phosphates concentration) within prescribed limits so that steam quality is not likely to be affected. In intermittent blowdown, a large diameter line is opened for a short period of time, the time being based on a thumb rule such as “once in a shift for 2 minutes”. Intermittent blowdown requires large short-term increases in the amount of feed water put into the boiler, and hence may necessitate larger feed water pumps than if continuous blowdown is used.

Continuous Blowdown

There is a steady and constant dispatch of a small stream of concentrated boiler water and replacement by a steady and constant inflow of feed water. This ensures constant TDS and steam purity at a given steam load. Once the blowdown valve is set for given conditions, there is no need for regular operator intervention. Even though large quantities of heat are wasted, an opportunity exists for recovering this heat by blowing into a flash tank and generating flash steam.

Benefits of Blowdown

Good boiler blowdown control can significantly reduce treatment and operational costs that include:

  • Lower pretreatment costs
  • Less make-up water consumption
  • Reduced maintenance downtime
  • Increased boiler life
  • Lower consumption of treatment chemicals

Stack Temperature

The stack temperature should be as low as possible. However, it should not be so low that water vapor in the exhaust condenses on the stack walls. It also indicates the scaling of heat transfer/recovery equipment and hence the urgency of taking an early shutdown for water/flue side cleaning.

Feed Water Preheating using Economizer

Typically, the flue gases leaving a modern 3-pass shell boiler are at temperatures of 200 to 300 °C.

Combustion Air Preheat

Combustion air preheating is an alternative to feed water heating. In order to improve thermal efficiency by 1%, the combustion air temperature must be raised by 20 °C.

Incomplete Combustion

Incomplete combustion can arise from a shortage of air, a surplus of fuel, or poor distribution of fuel. It is usually obvious from the color of smoke and must be corrected immediately.

Excess Air Control

Excess air is required in all practical cases to ensure complete combustion, to allow for the normal variations in combustion, and to ensure satisfactory stack conditions for some fuels.

Radiation and Convection Heat Loss

The external surfaces of a shell boiler are hotter than the surroundings. The surfaces thus lose heat to the surroundings depending on the surface area and the difference in temperature between the surface and the surroundings. The heat loss from the boiler shell is normally a fixed energy loss, irrespective of the boiler output.

Automatic Blowdown Control

Uncontrolled continuous blowdown is very wasteful. Automatic blowdown controls can be installed that sense and respond to boiler water conductivity and pH.

Reduction of Scaling and Soot Losses

In oil and coal-fired boilers, soot buildup on tubes acts as an insulator against heat transfer. Any such deposits should be removed on a regular basis. Elevated stack temperatures may indicate excessive soot buildup.

Reduction of Boiler Steam Pressure

This is an effective means of reducing fuel consumption, if permissible, by as much as 1 to 2%. Lower steam pressure gives a lower saturated steam temperature and, without stack heat recovery, a similar reduction in the temperature of the flue gas temperature results.

Variable Speed Control for Fans, Blowers, and Pumps

Variable speed control is an important means of achieving energy savings. Generally, combustion air control is effected by throttling dampers fitted at forced and induced draft fans.

Effect of Boiler Loading on Efficiency

The maximum efficiency of the boiler does not occur at full load, but at about two-thirds of the full load. If the load on the boiler decreases further, efficiency also tends to decrease.

Proper Boiler Scheduling

Since the optimum efficiency of boilers occurs at 65–85% of full load, it is usually more efficient, on the whole, to operate a fewer number of boilers at higher loads than to operate a large number at low loads.

Boiler Replacement

The potential savings from replacing a boiler depend on the anticipated change in overall efficiency. A change in a boiler can be financially attractive if the existing boiler is:

  • Old and inefficient
  • Not capable of firing cheaper substitution fuel
  • Over- or under-sized for present requirements
  • Not designed for ideal loading conditions

HVAC System

Heating, Ventilation, and Air Conditioning (HVAC) systems control the indoor environment (temperature, humidity, airflow, and air filtering). Comfort requirements that are typically impacted by the HVAC system include:

  • Dry-bulb temperature (Temperature of air measured by a thermometer freely hanged)
  • Humidity
  • Air movement
  • Fresh air
  • Cleanliness of the air
  • Noise levels

For generalizing the HVAC system, it can be dissected into five system loops:

  1. Airside loop
  2. Chilled water loop
  3. Refrigeration loop
  4. Heat rejection loop
  5. Control loop

Airside Loop

The first component of this loop is the conditioned space. The first two comfort requirements mentioned were dry-bulb temperature and humidity. In order to maintain the dry-bulb temperature in the conditioned space, heat (referred to as sensible heat) must be added or removed at the same rate as it leaves or enters the space. In order to maintain the humidity level in the space, moisture (sometimes referred to as latent heat) must be added or removed at the same rate as it leaves or enters the space. To determine how much supply air is needed for a given space, and how cold and dry it must be, it is necessary to determine the rate at which sensible heat and moisture (latent heat) enter, or are generated within, the conditioned space.

Chilled Water Loop

Chilled water systems in residential HVAC systems are extremely rare. A typical chiller uses the process of refrigeration to chill water in a chiller barrel. This water is pumped through chilled water piping throughout the building where it will pass through a coil. Air is passed over this coil and the heat exchange process takes place. The heat in the air is absorbed into the coils and then into the water. The water is pumped back to the chiller to have the heat removed. It then makes the trip back through the building and the coils all over again.

Refrigeration Loop

The refrigeration system removes heat from an area that is low-pressure, low temperature (evaporator) into an area of high-pressure, high temperature (condenser). It mainly has the following components:

  1. Evaporator (This is the coil that is inside of the house. Warm air will pass over the coil which contains the refrigerant, then the refrigerant absorbs the heat, then you are left with cold air which is distributed to the rooms that you are trying to cool).
  2. Compressor (What it does is it will circulate refrigerant throughout the whole system. It will compress cold vapor into hot vapor, it also increases the low vapor pressure into high vapor pressure).
  3. Condenser (This is the coil that is located outside on a central air conditioning system. It removes the heat that is carried through the refrigerant, forcing the hot air out).
  4. Metering Device (Controls the flow of the refrigerant to the evaporator).

Coefficient of Performance

The ratio of work or useful output to the amount of work or energy input is called the coefficient of performance. It is used generally as a measure of the energy-efficiency of air conditioners, space heaters, and other cooling and heating devices. COP equals heat delivered (output) in British thermal units (Btu) per hour divided by the heat equivalent of the electric energy input (one watt = 3.413 Btu/hour) or, alternatively, energy efficiency ratio divided by 3.413. The higher the COP, the higher the efficiency of the equipment. Higher COPs equate to lower operating costs. The COP usually exceeds 1.

COP = Q/W

Difference between COP and Efficiency

Both efficiency and COP are trying to give you the performance value of the system, whether it is a refrigerator or engine, where it involves input and output energies. But the difference is what types of energies are involved. There are two types of energies namely, High Grade Energy and Low-grade Energy. For efficiency, the ratios are between (1-(heat out/ heat supplied)) same form of energies. That is heat, low-grade energy. So it can never be greater than 1. Whereas the COP deals with the ratio between (heat removed / electricity supplied) both are different types. Electricity is a high-grade energy. And hence the COP is greater than 1.

Factors Affecting Performance & Energy Efficiency of Refrigeration Plants
  • Design of Process Heat Exchangers
  • Maintenance of Heat Exchanger Surfaces
  • Multi-Staging For Efficiency
  • Matching Capacity to System Load
  • Capacity Control and Energy Efficiency
  • Multi-level Refrigeration for Plant Needs
  • Chilled Water Storage
  • System Design Features

There is a tendency of the process group to operate with high safety margins which influences the compressor suction pressure/evaporator set point. For instance, a process cooling requirement of 15°C would need chilled water at a lower temperature, but the range can vary from 6°C to say 10°C. At 10°C chilled water temperature, the refrigerant side temperature has to be lower, say –5°C to +5°C. The refrigerant temperature, again sets the corresponding suction pressure of refrigerant which decides the inlet duty conditions for work of compression of the refrigerant compressor.

Maintenance of Heat Exchanger Surfaces

Effective maintenance holds the key to optimizing power consumption. Heat transfer can also be improved by ensuring proper separation of the lubricating oil and the refrigerant, timely defrosting of coils, and increasing the velocity of the secondary coolant (air, water, etc.). However, increased velocity results in larger pressure drops in the distribution system and higher power consumption in pumps/fans. Therefore, careful analysis is required to determine the most effective and efficient option.

Multi-Staging for Efficiency

Efficient compressor operation requires that the compression ratio be kept low, to reduce discharge pressure and temperature. For low-temperature applications involving high compression ratios, and for wide temperature requirements, it is preferable (due to equipment design limitations) and often economical to employ multi-stage reciprocating machines or centrifugal/screw compressors. Multi-staging systems are of two types: compound and cascade – and are applicable to all types of compressors.

Multi-stage Compressors

Reciprocating/piston compressors use a cylinder to force air into a chamber, where it is compressed. The simplest compressor designs feature a single cylinder/chamber arrangement. While straightforward, this setup is limited in its efficiency and capacity for delivering high volumes of pressurized air. That’s where multi-stage compressors come in. By increasing the number of cylinder stages, these machines work more effectively and can handle more tools at once.

Matching Capacity to System Load

During part-load operation, the evaporator temperature rises and the condenser temperature falls, effectively increasing the COP. But at the same time, deviation from the design operation point and the fact that mechanical losses form a greater proportion of the total power negate the effect of improved COP.

Capacity Control and Energy Efficiency

The capacity of compressors is controlled in a number of ways like on/off control, bypass or spill-back method, constant-speed step control, clearance volume control, valve control, etc. Capacity control of a refrigeration plant can be defined as a system that monitors and controls the output of the plant as per the load on demand.

Multi-level Refrigeration for Plant Needs

The selection of refrigeration systems also depends on the range of temperatures required in the plant. For diverse applications requiring a wide range of temperatures, it is generally more economical to provide several packaged units (several units distributed throughout the plant) instead of one large central plant. Another advantage would be the flexibility and reliability accorded. The selection of packaged units could also be made depending on the distance at which cooling loads need to be met. Packaged units at load centers reduce distribution losses in the system.

Energy Saving Opportunities of Refrigeration Plants

a) Cold Insulation

When a cold fluid is being transported through a system exposed to the ambient air, heat is being transferred from the air into the fluid in the system and the following occurs:

  • A temperature drop across the surface air film on the jacketing material
  • A further temperature drop across the insulation system
  • Yet a further temperature drop across the containing material
  • And finally another temperature drop across the fluid film into the fluid itself.

To avoid all the above causes, cold insulation should be done.

c) Building Heat Loads Minimization

Minimize the air conditioning loads by measures such as roof cooling, roof painting, efficient lighting, pre-cooling of fresh air by air- to-air heat exchangers, variable volume air system, optimal thermo-static setting of temperature of air-conditioned spaces, sun film applications, etc.

d) Process Heat Loads Minimization

Minimize process heat loads in terms of TR capacity as well as refrigeration level, i.e., temperature required, by way of:

i) Flow optimization

ii) Heat transfer area increase to accept higher temperature coolant

iii) Avoiding wastages like heat gains, loss of chilled water, idle flows.

iv) Frequent cleaning/de-scaling of all heat exchangers

e) At the Refrigeration A/C Plant Area

i. Ensure regular maintenance of all A/C plant components as per manufacturer guidelines.

ii. Ensure adequate quantity of chilled water and cooling water flows, avoid bypass flows by closing valves of idle equipment.

iii. Minimize part load operations by matching loads and plant capacity on line; adopt variable speed drives for varying process load.

iv. Make efforts to continuously optimize condenser and evaporator parameters for minimizing specific energy consumption and maximizing capacity.

v. Adopt VAR system where economics permit as a non-CFC solution.

Introduction to Waste Heat Recovery System

Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then “dumped” into the environment even though it could still be reused for some useful and economic purpose. The essential quality of heat is not the amount but rather its “value”. The strategy of how to recover this heat depends in part on the temperature of the waste heat gases and the economics involved.

A large quantity of hot flue gases is generated from Boilers, Kilns, Ovens, and Furnaces. If some of this waste heat could be recovered, a considerable amount of primary fuel could be saved.

Benefits of Waste Heat Recovery

Benefits of ‘waste heat recovery’ can be broadly classified into two categories:

Direct Benefits:

Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected by a reduction in the utility consumption & costs, and process cost.

Indirect Benefits:

a) Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide gas, sour gas, carbon black off gases, oil sludge, Acrylonitrile, and other plastic chemicals, etc, releasing to the atmosphere if/when burnt in the incinerators serves a dual purpose i.e. recovers heat and reduces the environmental pollution levels.

b) Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to a reduction in the flue gas produced. This results in a reduction in equipment sizes of all flue gas handling equipment such as fans, stacks, ducts, burners, etc.

c) Reduction in auxiliary energy consumption: Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption like electricity for fans, pumps, etc.

Analysis of Waste Heat Recovery for Energy Saving Opportunities

In any heat recovery situation, it is essential to know the amount of heat recoverable and also how it can be used. An example of the availability of waste heat is given below:

In a heat treatment furnace, the exhaust gases are leaving the furnace at 900 °C at the rate of 2100 m3/hour. The total heat recoverable at 180°C final exhaust can be calculated as:

Q = V ×ρ × Cp × ΔT

  • Q is the heat content in kCal
  • V is the flow rate of the substance in m3/hr
  • ρ is the density of the flue gas in kg/m3
  • Cp is the specific heat of the substance in kCal/kg °C
  • ΔT is the temperature difference in °C

Cp (Specific heat of flue gas) = 0.24 kCal/kg/°C

Heat available (Q) = 2100 × 1.19 × 0.24 × (900-180) = 4,31,827 kCal/hr

By installing a recuperator, this heat can be recovered to pre-heat the combustion air. The fuel savings would be 33% (@ 1% fuel reduction for every 22 °C reduction in the temperature of flue gas).

Commercial Waste Heat Recovery Devices

  • a) Recuperator
  • b) Radiation/Convective Hybrid Recuperator
  • c) Ceramic Recuperator
  • d) Regenerator
  • e) Heat Wheels
  • f) Heat Pipe
  • g) Economizer
  • h) Thermocompressor
  • i) Direct Contact Heat Exchanger

Recuperators

In a recuperator, heat exchange takes place between the flue gases and the air through metallic or ceramic walls. Duct or tubes carry the air for combustion to be pre-heated, the other side contains the waste heat stream. The simplest configuration for a recuperator is the metallic radiation recuperator, which consists of two concentric lengths of metal tubing.

Radiation/Convective Hybrid Recuperator

For maximum effectiveness of heat transfer, combinations of radiation and convective designs are used, with the high-temperature radiation recuperator being first followed by a convection type. These are more expensive than simple metallic radiation recuperators but are less bulky.

Ceramic Recuperator

The principal limitation on the heat recovery of metal recuperators is the reduced life of the liner at inlet temperatures exceeding 1100°C. In order to overcome the temperature limitations of metal recuperators, ceramic tube recuperators have been developed whose materials allow operation on the gas side to 1550°C and on the preheated air side to 815°C on a more or less practical basis.

Regenerator

Regeneration, which is preferable for large capacities, has been very widely used in glass and steel melting furnaces. Important relations exist between the size of the regenerator, time between reversals, thickness of brick, conductivity of brick, and heat storage ratio of the brick.

Heat Wheels

A heat wheel is finding increasing applications in low to medium-temperature waste heat recovery systems. It is a sizable porous disk, fabricated with material having a fairly high heat capacity, which rotates between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. The axis of the disk is located parallel to, and on the partition between, the two ducts. As the disk slowly rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot air and, as the disk rotates, from the disk to the cold air.

Heat Pipe

A heat pipe can transfer up to 100 times more thermal energy than copper, the best-known conductor. In other words, a heat pipe is a thermal energy absorbing and transferring system and has no moving parts and hence requires minimum maintenance. The Heat Pipe comprises three elements – a sealed container, a capillary wick structure, and a working fluid.

Economizer

In the case of a boiler system, an economizer can be provided to utilize the flue gas heat for preheating the boiler feed water. On the other hand, in an air pre-heater, the waste heat is used to heat combustion air. In both cases, there is a corresponding reduction in the fuel requirements of the boiler.

Shell and Tube Heat Exchanger

When the medium containing waste heat is a liquid or a vapor that heats another liquid, then the shell and tube heat exchanger must be used since both paths must be sealed to contain the pressures of their respective fluids. The shell contains the tube bundle, and usually internal baffles, to direct the fluid in the shell over the tubes in multiple passes. The shell is inherently weaker than the tubes so that the higher-pressure fluid is circulated in the tubes while the lower-pressure fluid flows through the shell. When a vapor contains the waste heat.

Plate Heat Exchanger

The cost of heat exchange surfaces is a major cost factor when the temperature differences are not large. One way of meeting this problem is the plate type heat exchanger, which consists of a series of separate parallel plates forming thin flow pass. Each plate is separated from the next by gaskets and the hot stream passes in parallel through alternative plates whilst the liquid to be heated passes in parallel between the hot plates. To improve heat transfer the plates are corrugated.

Run Around Coil Exchanger

It is quite similar in principle to the heat pipe exchanger. The heat from hot fluid is transferred to the colder fluid via an intermediate fluid known as the Heat Transfer Fluid. One coil of this closed loop is installed in the hot stream while the other is in the cold stream. Circulation of this fluid is maintained by means of a circulating pump.

Waste Heat Boilers

Waste heat boilers are ordinarily water tube boilers in which the hot exhaust gases from gas turbines, incinerators, etc., pass over a number of parallel tubes containing water. The water is vaporized in the tubes and collected in a steam drum from which it is drawn off for use as heating or processing steam. Because the exhaust gases are usually in the medium temperature range and in order to conserve space, a more compact boiler can be produced if the water tubes are finned in order to increase the effective heat transfer area on the gas side.

Thermocompressor

In many cases, very low-pressure steam is reused as water after condensation for lack of any better option of reuse. In many cases, it becomes feasible to compress this low-pressure steam by very high-pressure steam and reuse it as medium-pressure steam. The major energy in steam is in its latent heat value and thus thermocompressing would give a large improvement in waste heat recovery. The thermocompressor is a simple equipment with a nozzle where HP steam is accelerated into a high-velocity fluid.