Power Connect Newsletter

BY DAN BARBERSEK
Director of Energy Management Solutions, Generac Power Systems


INTRODUCTION
Do natural gas engine generators have a place within the onsite fuel storage discussion? This is being examined due to the overall growing desire of utilizing natural gas as the preferred fuel supply for onsite power generation. When looking at the storage of natural gas onsite, engineering, financial and regulatory challenges must be considered when it comes to emergency generator operations.


UTILIZING NATURAL GAS
According to research done by Frost & Sullivan, the use of natural gas for onsite power generation has grown 10% in the last ten years. Several driving factors can help explain this growth over the use of diesel fuel include:

• Customer Preference – Environmental concerns both owning and maintaining diesel fuel, as well as emissions concerns and permitting fall squarely upon the end user.

• Diesel Fuel Cost of Ownership – The new low sulfur fuel is more prone to microorganism growth, which has a direct effect on fuel reliability. Strong ongoing maintenance plans and fuel polishing systems’ cost or fuel replacement programs must be accounted for.

• Fuel Delivery – When a major event strikes, such as hurricanes and flooding, getting diesel fuel delivered over damaged roads can be a major hurdle to overcome as well as supply and demand constraints.

The use of natural gas bypasses these three major challenges, but it comes with other considerations. Delivery reliability is commonly a concern when it comes to natural gas. This comes even though the performance of our natural gas delivery system in the United States has far outperformed the electrical grid year after year. MIT Lincoln Laboratory conducted one of the more comprehensive studies, “Interdependence of the Electricity Generation System and the Natural Gas System and Implications for Energy Security”, in May 2013 to support this claim. This study concluded that the natural gas distribution system operates at a reliability of over 99.999%. On top of this, natural gas will flow if all electric utilities shut down for several months. The study said this is due to several factors; one being that many of the natural gas compressor stations run off natural gas, and the total volume of gas piping (4 trillion cubic feet) currently in the system.

Even with strong delivery systems, the use of natural gas becomes limited especially when it comes to generators that are supporting life safety loads. Both the NFPA, and the NEC within the NFPA, reference the requirement of on-site fuel as well as site approval from local Authority Having Jurisdiction (AHJ) to utilize this fuel for life safety applications.


NATURAL GAS STORAGE
Due to the activity of the transportation sector, natural gas storage technology is experiencing tremendous growth.

Compressed Natural Gas (CNG)
CNG storage for industrial applications dates back to the 1940s. The approach is currently favored by the transportation industry. CNG is generally stored in high-pressure cylinders, typically at 3,600 lb/in2 for mobile applications. At 3,600 lb2, the volume of natural gas is reduced by a factor of 296 compared to atmospheric pressure; or a storage efficiency of 296 V/V. The V/V ratio represents the volume gas at standard temperature and pressure compared to the storage volume. Type I cylinders are the most common for CNG and are made of steel. These cylinders are susceptible to corrosion if the moisture level of the gas is
high. Due to their high pressure, their size, shape and material
are very limited.

Absorbed Natural Gas (ANG)
Adsorption storage is based on the properties of natural gas referred to as the ads=orbate and the adsorbent, which is typically a carbon, graphene or metal-oxide. These properties give the adsorbent the ability to store the gas ten to hundreds of times the amount of gas given the volume and pressure compared to CNG. The ultimate goal of ANG technology is to safely store natural gas in the minimum volume at a pressure not exceeding 500 lb/in2. Filling the tanks does need to be examined. If the “fast fill” (5-10 minutes) method is used, the heat that is caused utilizing this method must be managed. When looking at using this technology for an Emergency Power System (EPS), these concerns are diminished. This is due to how these tanks will be utilized in this type of application. Once the tanks are initially filled, and will stay that way for long periods, they will not need to be filled again until the following two simultaneous conditions are met, loss of utility and loss of the natural gas supply.

Breaking down the numbers for these conditions looks like the following (assuming the utility has a 99% availability and the natural gas has a 99.9% availability.
 
This will give the EPS of 99.999% availability that either the utility or the natural gas will be present during an event to run. It is also important to remember that the loss of utility will have no bearing on these tanks, only when both utility and natural gas are lost.

Cost
Cost on EPS is driven directly by kW size so for this costing example we will assume a 500kW natural gas generator with a two hour back up supply requirement. Using the CNG approach with high-pressurized cylinders will cost around $33,000. A standard UL 142 double wall diesel fuel tank (1000 Gal) will cost about $21,500. Currently, there are no manufacturers that make ANG tanks for this size as this technology is coming out of the vehicle market, but today’s cost comparisons are coming in at around ~$150/CF. Their target goal to make this technology a viable solution would be to get this manufacturing cost down to $55/CF. (Please note that these costs do not reflect the natural gas compressor)

Codes
NFPA 52 is restricted to vehicle fuel systems, their associated fueling and gas storage systems. It is not intended to cover stationary equipment such as emergency generators. NFPA 55 does provide guidance for CNG or ANG storage systems as applied to an EPS but it may be helpful until other codes and standards adapt. NFPA 54 – which encompasses the National Fuel Gas Code, does not directly address CNG or ANG systems. Paragraph 1.1.1.2 specifically exclude gas generators and compressors. Some requirements will affect the use of ANG as an on-site stored fuel. In addition, paragraph 5.3.2.1 does reference interconnections for standby gas. Therefore, as this technology goes, the codes will have to adapt to this growth.

End Game – Reliability
While there are many positive reasons for using natural gas for on-site power generation, the key and most important factor is overall system reliability. For many years, this meant diesel-powered generators with onsite diesel fuel storage tanks, but diesel fuel grade (low Sulfur) requirements and disaster frequency and severity continues to challenge this statement. Region history must be thoroughly examined along with education and knowledge regarding incoming technologies.

For more information about these concepts or the variety of Generac products available, contact Generac Power Systems at www.generac.com or toll free at 1-844-ASK-GNRC.



Author Background
Dan Barbersek is the Director of Energy Management Solutions for Generac Industrial Solutions with over 38 years of experience in the energy industry as an application engineer—including 18 years in the UPS industry—he has a thorough knowledge of power technologies, from the conventional to the cutting edge. He has served in the United States Navy, where he completed Electrician’s Mate “A” School, and is a member of IEEE, 7x24 User Group, EGSA and the North Carolina Healthcare Engineering Association.