Copyright © 2005 Advantica Inc. (USA Only) and Advantica Ltd. (Outside USA). All rights reserved by the respective owner.

Own Use Gas

Review of 2000 Model

Overview

• Summary of 2000 OUG project• Information and data• Model overview• Original assumptions and recommendations• Pre-heater energy losses overview• Uncertainties

• Shipper concerns• Possible solutions• Initial recommendations

• Seeking a collaborative approach to estimation of OUG

Shrinkage

• Based on overall throughput• Leakage from low pressure network• Own Use Gas for pre-heaters• Theft of Gas

• Advantica carried out study into the estimation of OUG in 2002 using data from 2000

The methodology and model

• Typical PRS layout

Information and data

• All NTS and LTS sites using pre-heating • Flow, inlet, outlet pressure, exit temperature • Data unavailable for some LDZs

• Basic pre-heater meter readings from ~80 sites• Generally poor quality

• Total system throughput• Pre-heater survey data

• Site name, location etc• Operational measurements/limits

• Ground temperatures – from work on statistical analysis of national and regional temperatures (2000)

Information and data cont…

• The percentage of sites from which suitable data was acquired was:

• NTS: 64% - missing data for West Midlands LDZ North Wales LDZ

• LTS: 34% - missing data for East Anglia, North West, and Scotland LDZs

• Giving an overall site coverage of 42% for hourly data over the year 2000.

• Over 3Gb of data was received, filtered and processed

The methodology and model

• The method is based around the equation

• Where:• is the mass flow rate (kg/h),

• is the rise in temperature in the heater (deg C),

• is the specific heat capacity of the gas (kJ/kg/K),

• is the efficiency of the heater and

• is the energy used in the heater (in kJ/h)

1

)/( CpmhkJP T

mT

Cp

P

Assumptions

• Initial gas inlet temperatures set to Ground Temperature data for each LDZ throughout the year• Outlet temperature set to 0 deg C if no set-point available

• Heaters are operational throughout the year

• Preheat requirements are assigned to each station rather than by heater

• LDZ pre-heater efficiencies are the same as NTS pre-heater efficiencies.

Assumptions cont…

• OUG usage estimated for missing LDZs using monthly scaling factor based on other LDZ data

• A range of Hot Water Bath pre-heat efficiencies used in analysis• Used a figure of 50% based on previous OUG model assumptions

and research reports

Hot Water Bath Efficiencies

• E7 Transco technical Specification for Gas Fired Water Bath Heaters Part 1 Basic Heater requirements 1993.• “Heat loss in flue gases shall not exceed 25% of gross heat input.”• “Heat losses from outer shell and associated gas pipe work shall

not exceed 1% of the declared heater output.”

• Thermal efficiency of Water Bath Heaters at Alrewas AGI MRS 403• Efficiencies under various operating conditions between 53 and

66%

• Efficiency tests on Water Bath Heaters at Coleshill AGI MRS I 2912 • Quotes range 58 to 66.5%

Typical Water Bath Heater

OHT 9.1

Surface losses 0.5-1%

Flue Losses

25-40%

Hot Water Bath Energy Losses

• A number of studies carried out in the early 80’s

• Main energy losses via flue gas in the heating process

• Surface losses account for 0.5-1% total energy lost

• Highlighted that most pre-heaters operated below design efficiency (design efficiency typically around 70%)• Typically 30-42% in flue losses

• Experiments showed this could be improved with correct burn/air flow rates

Model Validation 2000

0.00E+00

1.00E+06

2.00E+06

3.00E+06

4.00E+06

5.00E+06

6.00E+06

7.00E+06

8.00E+06

9.00E+06

1/4

/00

2/4

/00

3/4

/00

4/4

/00

5/4

/00

6/4

/00

7/4

/00

8/4

/00

9/4

/00

10/4

/00

11/4

/00

12/4

/00

Months

kW

Hrs

Towton A+B+C

0.00E+00

5.00E+05

1.00E+06

1.50E+06

2.00E+06

2.50E+06

3.00E+06

3.50E+06

4.00E+06

4.50E+06

Jan-00

Feb-00

Mar-00

Apr-00

May-00

Jun-00

Jul-00

Aug-00

Sep-00

Oct-00

Nov-00

Dec-00

Months

kWH

rsTowton

OUG Usage

Efficiency Total Flow (kWh)

Total OUG (kWh)

% OUG

100% 7.13E+11 4.03E+07 0.0057

70% 7.13E+11 5.76E+07 0.0081

60% 7.13E+11 6.72E+07 0.0094

50% 7.13E+11 8.07E+07 0.0113

40% 7.13E+11 1.01E+08 0.0141

30% 7.13E+11 1.34E+08 0.0188

Uncertainties

• Pre-heater efficiencies

• Control regime of pre-heaters

• Ground temperature assumptions

• Scaling factor to estimate pre-heater consumptions for LDZs with missing data

Uncertainties cont…

• 95% confidence intervals attributed to missing data

• 0.0102% (assuming a heater efficiency of 50%).

and

• 0.0137% (assuming a heater efficiency of 50%).

• Including variation in efficiency of the pre-heaters, the actual OUG percentage figure may lie between:

• 0.0073% (with 70% efficiency) and

• 0.0229% (with 30% efficiency)

Recommendations 2002

• Better estimation of pre-heater efficiencies

• Include control strategies for pre-heaters

• Improve mapping of sites with pre-heat and incomplete telemetry to similar sites

• Extend metering of pre-heaters to improve model validation

Summary of Shipper Concerns

• Original study is 4 years old, data is 6 years old and likely to be out of date

• Limited data impacts the accuracy of the model

• Real pre-heater efficiencies are much lower than quoted in report

• Insufficient meter readings to properly validate the model

Solutions – Age of the model

Investigate

model sensitivity

Large variation

in % OUG

Model suitable

for other years

partial analysis

using 2005

data for 3-4 LDZs

Small %OUG

variation

Review findings,

potentially do

remaining LDZs

Solutions – impact of missing data

Investigate

model sensitivity

No - need

improvement plan

partial analysis

using 2005

data for 3-4 LDZs

Has data

quantity/quality

improved for

key variables?

Review findings,

potentially do

remaining LDZs

Solutions – pre-heater efficiencies

• Summarise findings of previous pre-heater efficiency trials• Covers various pre-heater efficiency tests • Provides evidence of typical pre-heater efficiencies from the

output of the experiments conductedProvides information needed to carry out on-site efficiency tests

• Carry out pre-heater efficiency tests• Requires on-site monitoring equipment • Timeline significant as tests require variety of operating conditions• Use efficiencies to validate the model• Test pre-heaters makes/models that are most commonly installed

• Use OUG model to calculate efficiencies

Alternative solution – use model

Site flows,

pressures,

temperatures

Pre-heater

metering

Compare OUG

vs consumption

Determine Hot

Water Bath

efficiency

Use model to

calculate OUG

Solutions - validating the model

Site flows,

pressures,

temperatures

Pre-heater

metering

Determine Hot

Water Bath

efficiency

Compare OUG

vs consumption

Use model to

calculate OUG

Initial Recommendations

• Model sensitivity analysis

• Summary of pre-heater efficiency work• And/or• Validate model by carrying out pre-heater efficiency tests

on sites with good telemetry and metering

• Determine pre-heater efficiencies using wider sample of meter readings assuming model correct

• Report findings and present back to forum