X Международная студенческая научная конференция Студенческий научный форум - 2018

Companies in most industries require a back-up system for their primary energy source when there is a risk of energy interruption or when there is a significant economic benefit. This holds true especially for companies using natural gas that have loads greater than 2 million Btu/Hour.

Many industrial processes operate continuously. Fuel interruption halts mass production and as a result major economic losses are incurred. In some cases, as it is in the Glass Industry, fuel interruptions are devastating. Fuel shortage not only results in production losses, there are also hundreds of thousands of dollars lost in capital investments. Covering this risk with a back-up fuel system is a requirement.

The goal for companies in all industries is to be in a competitive position. Seeking a reliable and environmentally friendly energy source that will also offer the lowest possible manufacturing costs can put them ahead of the game. Propane-air back-up systems allow companies to benefit from interruptible Natural Gas rates while relying on environmentally clean fuel sources.

Propane-Air standby systems allow natural gas users the ability to have live back-up when ever required. Because propane air is a "synthetic natural gas" (SNG), it can be used as a direct substitute for natural gas. Unlike diesel, fuel oil or propane, SNG does not require additional gas trains, piping, regulators, or special fuel delivery systems inside the factory. The propane air mixture is simply connected to the natural gas piping just after the metering station (and pressure reducing station) but before entering the building(s). These systems can be placed in live back-up so that they take over upon falling pressure, or they can be turned on manually. In either the case it is akin to having an electrical generator.

There is no size limitation for these systems but generally speaking it is not economically feasible for loads less than 1-2 million Btu/hr.

Utility Peak Shaving with Propane-Air

A leading source of energy in the world today is Natural Gas. Expanding economies and the deployment of gas turbine electricity generation facilities increase the demand for natural gas, resulting in lower pipeline and distribution pressures and the need for additional investment in pipelines, distribution grids, and operating wells. High winter demands also put a strain on natural gas distribution. Natural Gas LDC's have a limited number of options available to help balance and minimize the effects of these constraints - the use of storage buffers and peak shaving systems are two primary examples.

When it comes to peak shaving there are two choices - LNG and Propane-Air. A typical propane-air peak shaving plant consists of LPG storage facilities, truck unloading station, transfer pumps, propane vaporizers, air compressors, propane-air mixer, gas flow rate and calorific value measurement device, and system controls. The benefits of propane-air peak shaving over using LNG are significantly lower capital investment, ease of fuel storage and lower maintenance costs. The drawback to using propane-air is the higher cost of fuel and the need for compressed air when mixing. In most cases the differential in initial capital investment is so extreme that propane-air peak shaving systems are favored.»[1]

WHAT IS A LPG STANDBY PLANT?

«A "standby plant" - as the term implies, is something standing by to do a job. A Propane standby plant, offered to industrial and utility users of NatGas, is a system that is an alternate source of energy in the event the NatGas source becomes unavailable (because of curtailment, maintenance shutdown, or catastrophic failure).

While some facilities use oil as a standby fuel, oil is not a direct replacement for NatGas and will not burn in NatGas burners or equipment. Thus, oil requires a separate set of burners, controls and piping (which increases the equipment cost).

Propane or LPG is an ideal standby fuel for NatGas. Propane, when mixed with air, will duplicate the burning characteristics of NatGas and allows the user to utilize existing NatGas burners, piping and controls. There is generally no need to change the setup of the combustion equipment when the fuel supply changes from NatGas to LP/air, or from LP/air to NatGas.

A standby system generally consists of:

LPG STORAGE TANK(s);

A PUMP to transfer LPG to the Vaporizer;

A VAPORIZER to convert the liquid LPG to a gas;

A MIXER or BLENDER to mix the vaporized LPG with air.

WHY USE A STANDBY SYSTEM?

While there are many reasons a standby system is used, the principal reason is insurance against interruption of normal NatGas supply. Another incentive is that many utility companies offer what is known as an "interruptible rate" to industrial customers.

First - interruption of NatGas?

Many are not aware that NatGas utilities (local distribution companies [LDC]) purchase or contract from a pipeline, a certain amount of NatGas transportation capacity for a certain period. The contracted capacity has to be sufficient to supply all "firm gas" customers (both residential and industrial) on the coldest day of the year. By definition, this means that the contracted transportation capacity is under-utilized during the other 364 days in a year.

To better utilize the contracted transportation capacity, LDCs like to add large gas users as "interruptible" load. If the pipeline capacity that is normally occupied by the interruptible customers is needed to supply gas to "firm" customers, the LDCs ask their interruptible customers to stop using NatGas and to switch to their LP/Air standby system.

As an incentive for these interruptible customers to install a standby system, the LDCs offer steep discounts on the price of NatGas. The savings are available year-round, regardless whether or not the NatGas is ever curtailed.

Since the "interruptible rate" is enjoyed every day of the year, not just during cold months when gas is most critical, it is possible to amortize the cost of a standby facility, including the installation, over a very short period of time, usually in less than two years, in some cases in as little as 6 months..

With a useful life of a standby system of 15-25+ years, this means that significant energy cost savings are being realized by the owner of the standby system year-after-year, with only upkeep and maintenance as recurring expenses.

WHAT IS A PEAKLOAD SHAVING PLANT?

Peakload Shaving is a term used by utility companies. As stated before, LDCs purchase a certain amount of gas over a fixed period of time. The best laid plans cannot take into consideration unexpected cold spells, a burst pipeline, or other events that could happen to disrupt the planned quota.

If the LDC should need more gas than it has contracted, they pay a premium price -- if the gas is available, to begin with. So, to insure extra gas and avoid premium price for gas above the contracted amount, many utility companies use LP, blended with air, to duplicate the properties of NatGas. This blended gas is then used to supplement the LDC's gas supply, allowing a more consistent fuel flow rate from their supplier and help meet peak demand loads.

WHO USES A STANDBY PLANT?

Utilities and municipalities; ceramics product manufacturers; glass plants; bakeries; metal processing firms; textile industries; chemical companies; or, any industrial company that uses large amounts of NatGas in any of its processes.

WHAT IS LP-GAS?

LP-Gas or LPG is the abbreviation for liquefied petroleum gas, with the most commonly known being Propane and Butane. At normal atmospheric pressure and temperatures, LP-Gas is in the gaseous state. However, it is converted to the liquid state with moderate pressure. This is why LPG is transported and stored in tanks or containers having at least 250 psi working pressure.

The main source of LPG is NatGas and crude oil mixtures as they come from active oil and NatGas wells. Though Propane is similar to NatGas (Methane), Propane has 2516 BTU per cubic foot (22390 kcal/m³), compared to 1020 BTU per cubic foot (9005 kcal/m³) for NatGas. That is why Propane, when mixed in proper proportion with air, is an excellent supplement or replacement to NatGas.

WHAT IS A LPG VAPORIZER?

As shown above, LPG (Propane, Butane, or Propane/Butane Mixture) at ambient pressure (above its boiling point temperature) is a gas that is stored in pressurized containers (tanks) in liquid form. The space in the tank that is not filled with liquid is occupied by vapor. As this vapor is being used as fuel for connected equipment (burners, heaters, etc.), liquid LPG must vaporize (change its state from liquid to gas) to occupy the space above the liquid.

Any time a change of state occurs, energy is required. If the ambient temperature is above the boiling point of the LPG (Propane -44°F / -42°C; Butane 32°F / 0°C at ambient pressure; see chart above for the boiling temperature of LPG at various pressures), this energy is transferred in the form of heat from the ambient air through the steel walls of the storage tank, into the LPG. As the heat is transferred from the ambient air to the vaporization process, the ambient air "looses" this energy and cools down.

The amount of heat that is transferred into the LPG determines the rate of vaporization. As the ambient air cools down, the rate of vaporization slows down, and stops completely when the ambient air is at the same temperature as the boiling point of the LPG. Therefore, naturally occurring vaporization cannot be used for large gas loads, or in low ambient temperatures.

A vaporizer is designed to receive the liquid LPG and raise its temperature (heat the liquid) well above the boiling point at the delivery pressure. In other words, a vaporizer generates the (heat)energy that is required to maintain the gaseous state of the LPG.

The heat required to change the state of the LP from liquid to gaseous is also called the latent heat of vaporization. Typical LPG requires a heat input of approximately 800 BTU to vaporize 1 gallon of liquid (approximately 100 kcal per kg of liquid). AES vaporizers are designed to generate approximately 1.5 times the latent heat of vaporization. The excess heat is carried by the LP vapor as superheat. Superheat is required to maintain the gaseous state of the LP downstream of the vaporizer.There are two major types of LPG vaporizers: Vaporizers that supply a small portion of the vaporized LPG as fuel for the burner that supplies the heat for the vaporization process (i.e. Water Bath Vaporizers); and vaporizers that use an outside source of heat, such as steam or hot water, to vaporize the LPG.

WHAT ARE MIXERS AND BLENDERS?

After the liquid Propane has been vaporized, it needs to be blended in proper proportion with air to duplicate the characteristics of NatGas. This is where mixers and blenders come in.

There are several methods to mix air and LPG vapor. Probably the most simple method is to use a venturi tube and a nozzle. This method, as well as other methods, holds very accurate air-to-fuel ratios through a narrow range. This type mixer does not generally require compressed air for operation. However, the maximum achievable system pressure is somewhat limited. The mixture of air and vapor is fed into a surge tank, where it is maintained at a set pressure, and then drawn from the surge tank for use. This type system is usually recommended for intermittent periods of use and is very simple to operate.

Blenders and modulating proportioning mixers are usually more complex, but are usually also more accurate than Venturi-type mixers. They are also capable of blending LP vapor with air in much larger volumes at much higher pressure. These systems are recommended for continuous or long periods of usage, and are ideally suited for PeakShaving and larger installations.

Regardless of the type vaporizer and blender, a standby system can be designed for the requirements of small users, or the requirements of large industrial and utility users. In times of uncertain oil prices and supplies, a standby system should be considered by all Natural Gas users. Just like we keep a spare tire for our automobile in the event of a flat, a standby system is a spare fuel supply in the event Natural Gas is interrupted or demand cannot be met.»[2]

«The mixing technology can be used as Back-up equipment or Gas costs Peak shaving.

Technology is also economic alternative.

ADVANTAGES:

Economic reasons (back-up system): uninterruptible gas service rates, better position to negotiate fuel cost with Natural Gas supplier.

Alternative solution: pipelines maintenance and servicing, global cut-off of gas (emergency back-up), standby solution for accidents at pipelines.

Supply a remote community with Natural Gas – permanent or temporary until extension of Natural Gas main.

LPG/AIR IS 100% INTERCHANGEABLE WITH NATURAL GAS:

Combustion characteristics of LPG/air are identical to Natural Gas.

NO modifications of Natural Gas equipment: no burner modifications, no orifice changes, no regulator or line adjustments.

You can switch to LPG/air immediately - NO pre-purging or post purging of the line.

LPG/air mixture can directly replace the natural gas in combustion applications.

When LPG is mixed with Air to the correct ratio, the resulting mixture will burn with the same characteristics as Natural Gas.

LPG/AIR MIXED RATIO:

OPERATION

In the basis of the system there are mixer and LPG vaporizer. Depending on its type the vaporizer uses electric or gas energy for transformation of LPG liquid to vapor. LPG vapor enters then the venturi mixer. As pressurized vapor passes through the mixer, the kinetic energy of the gas draws in air from the atmosphere through a check valve. The mixture is then re-pressurized through the diffuser before it enters the surge tank.For bigger capacities and higher discharge pressures the air is supplied through compressor and mixing process is digitally controlled.

Unlike diesel, fuel oil or propane, synthetic natural gas does not require additional gas trains, piping, regulators, or special fuel delivery systems inside the factory. The

propane air mixture is simply connected to the natural gas piping just after the metering station (and pressure reducing station) but before entering the building.

TYPES OF NG REPLACEMENT SYSTEMS

There are 3 types of system depending on mode of LPG vaporizing:

DFM (with Direct Fired vaporizer)	XPM (with XP electric vaporizer)	QM (with waterbath vaporizer)
Combination of Algas Direct Fired vaporizer, venturi mixer and LPG pump. Combination of Algas XP electric	Combination of Algas XP electric vaporizer, venturi mixer and LPG pump.	Combination of gas fired waterbath vaporizer, venturi mixer and LPG pump.

Capacity range: 2.5 to 28 MM Btu/h at delivery pressures from 5 to 12 psig for propane and 5 to 8 psig for butane atmospherically (with no compressor). • 100% turndown means these units are perfect for variable or steady loads. • The most economical solution to lower gas bills. • Available in 110V/50-60Hz or 220V/50-60Hz. Electrical consumption less than 1 amp. • Air inlet silencer (80dB at 10 feet).

Capacity range: 2.5 to 21 MM Btu/h at delivery pressures from 5 to 12 psig for propane and 5 to 8 psig for butane atmospherically (with no compressor). • 100% turndown capability • Able to make natural gas in less than one minute! • Venturi silencer • Explosion proof (Class I, Division 1, Group D)

Capacity range: 2.5 to 21 MM Btu/h at delivery pressures from 5 to 12 psig for propane and 5 to 8 psig for butane atmospherically (with no compressor). • Integrated PLC controlled operating system with user interface and on/off/standby modes. • Component cycle and runtime display • Air intake header with silencer

The 300mbar systems may require and underground tank. Higher pressure systems require a small liquid pump.»[3]

References

https://algas-sdi.com/resources/more-about-transportable-gases/what-is-propane-air

http://altenergy.com/Technology/Tech.htm

http://www.kadatec.cz/wp-content/uploads/2009/03/lpg-air-mixing-2-a3.pdf

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