MEASUREMENT OF THE LNG DELIVERED AND THE GAS REDELIVERED

Transcription

1 MEASUREMENT OF THE LNG DELIVERED AND THE GAS REDELIVERED 1) INTRODUCTION ) MEASUREMENT OF THE LNG DELIVERED ) DETERMINING THE AMOUNT OF LNG DELIVERED ) MEASUREMENT SYSTEM FOR THE LNG DELIVERED ) MANAGEMENT OF THE UNLOADING OF LNG VOLUMES THAT ARE GREATER THAN EXPECTED VOLUMES 4 3) MEASUREMENT OF THE GAS INSERTED INTO THE NETWORK ) DETERMINATION OF THE VOLUME OF GAS INSERTED INTO THE NETWORK ) SYSTEM FOR MEASURING THE VOLUME OF GAS INSERTED INTO THE NETWORK ) CHECKING OF INSTRUMENTS ) CONSUMPTION AND LOSSES

2 1) INTRODUCTION The amount of LNG, expressed in m 3, delivered by the User to the Operator at the Delivery Point and the determination of the volume of gas inserted into the network by the Operator at the interconnection with the Snam Rete Gas transportation network is measured according to the procedures in use at the Terminal, as described below. 2) MEASUREMENT OF THE LNG DELIVERED 2.1) Determining the amount of LNG delivered The volume of LNG in the LNG carrier's tanks is measured by taking into account a number of parameters, including a) onboard the Carrier, before unloading begins and again once unloading has been completed, the Volume of LNG in the tanks Temperature of the LNG Pressure of the gas phase in the tanks b) at the Terminal, as ascertained by the composition analysis performed by the gas chromatographs, the Density of the unloaded LNG Gross Heating Value of the LNG Wobbe index of the LNG Gross Heating Value of the Vapour Density of the vapour The volume of LNG and the energy unloaded shall be determined by means of a collective consultation between the ship's Captain (or his first officer as a delegate), a representative of the User, a representative of the Operator, the inspector of the surveying company and, as required, a Customs' representative, taking into account the following two measurements: the first measurement shall be taken after mooring and before the unloading arms are connected to the LNG carrier, while the unloading manifold valve is still closed, and after the ship s Captain, as required by procedure, has sent a notice of readiness to unload the LNG; the second measurement shall be carried out immediately after unloading has been completed and the manifold valve has been closed. The difference in value between the two LNG volumes, determined by the aforementioned measurement operations, net of any quantities of boil-off gas from the ship used during the unloading phase, shall be considered as the volume of LNG unloaded from the LNG carrier. 11-2

3 The parties mentioned above shall indicate their acceptance by signing the "Assessment Report" showing the quantity - and quality - of LNG unloaded, thus confirming their complete agreement with regard to the values used for all of the parameters mentioned above. The volume of LNG unloaded shall be converted into the equivalent amount of energy (expressed in MJ) on the basis of the Gross Heating Value determined according to the procedures outlined in the chapter entitled "Quality of the LNG delivered and the gas redelivered". 2.2) Measurement system for the LNG delivered The measurement of the LNG delivered - in terms of volume, temperature and pressure - is carried out according to the methods described below. The measurement of the volume of LNG is obtained by measuring the height of the LNG in the tanks, making the appropriate adjustments to obtain the correct height and then, using the appropriate calibration tables, calculating the volume of each tank. The height is measured at least 15 minutes after the Carrier has moored and 15 minutes after unloading has been completed. The adjustments applied to all level measurement systems - made to obtain the correct height of LNG, are carried out according to the floating conditions of the Carrier, as follows: Trim (forward draft/aft draft) List (heel) The corrections are individually tabulated for each tank and are expressed in millimetres according to the level and measurement of forward/aft draft for Trim and the degree of List. The millimetres of correction to be made are calculated from the tabulated values, using interpolation to arrive at the real values including the Trim and List values. The calibration tables, complete with all of the necessary adjustment tables, should meet ISO standards (in particular ISO for prismatic membrane tanks and ISO 9091/ or ISO 9091/ for spherical tanks). For each LNG carrier, the User must send the Terminal a certified copy of the tables with data expressed in metric units. Any physical change, distortion or change in volume of the tanks shall require a new calibration which must be certified, approved and delivered as described above. The certification of the instrument calibration is carried out in accordance with the Ship Approval Procedures, as defined in the chapter entitled "Methods and procedures for authorising the unloading of LNG carriers". Among other things, the procedure specifies that every three years, GNL Italia may request that the calibration certification of the LNG measurement instruments onboard the Carrier be updated. The Operator reserves the right to request such documentation at any time deemed appropriate. During the unloading phase, the User has the option to use the boil-off gas in the carrier's tanks as fuel. The amount of boil-off gas used during unloading must be measured with instruments that conform to applicable laws. This value is converted into energy using the Gross Heating Value of the Vapour. 11-3

4 In the event that the measurement system is not available, the energy associated with the Boil-Off gas used by the Carrier during unloading is set at 90 GJ per hour interval between the measurement tasks referred to in paragraph 2.1 above. The energy used by the ship for its own consumption shall be deducted for the purposes of determining the volume of LNG unloaded. The temperature of the LNG inside the Carrier's tanks is measured by temperature sensors. These sensors must be distributed along the height of the tanks with one permanently immersed in the LNG. The temperature of LNG in each tank is the average of the values of all of the sensors immersed in the liquid. The temperature of the entire load is obtained by calculating the overall average of the average temperature of each tank. Using the same methodology described for measuring the temperature of the LNG, the temperature of the vapour is obtained, taking the values transmitted from the temperature sensors that are not immersed in the LNG. The pressure measurement systems measure absolute pressure in bar or mm H 2 O. For load calculations, the pressure will be rounded up to 1 mbar or 1 mm H 2 O. The relative pressure of the vapour to atmospheric air is calculated using an atmospheric pressure value of bars. 2.3) Management of the unloading of LNG volumes that are greater than expected volumes In the event that a Carrier arrives at the Terminal with a volume of LNG that is greater than the expected volume to be unloaded (or the Maximum Unloading Capacity, in the case of spot unloading), the Operator shall carry out the appropriate checks to determine the feasibility of completing unloading operations for the cargo that is in excess of the expected volume, taking into consideration the space in the storage tanks and any impact it may have on the LNG delivery schedule. Where the outcome of such checks is positive, the Operator shall notify the User concerned by fax that it is possible to complete the unloading operations: where the outcome is negative, the Operator shall request the User to discontinue unloading when the LNG volume unloaded reaches the scheduled unloading volume (or the Maximum Unloading Capacity in the case of spot unloading operations). In the event that it is not possible to discontinue unloading operations for safety reasons, the provisions outlined in the chapter entitled "Receiving, storage and regasification of LNG", paragraph ("Failure to comply with the unloading window for reasons not attributable to the Operator") shall apply or, in the case of spot unloadings, the provisions outlined in paragraph ) MEASUREMENT OF THE GAS INSERTED INTO THE NETWORK The volume of gas inserted into the network for the purpose of delivery to the Virtual Exchange Point is determined accordance with the provisions of Article 7, paragraph 4 of Annex A to Resolution No. 185/

5 3.1) Determination of the volume of gas inserted into the network The volume of gas inserted into the network is determined at the measuring station, owned by GNL Italia and located at the interconnection with the Snam Rete Gas transportation network: this station is equipped with a suitable system that takes hourly readings of the measurement data collected. GNL Italia, in its capacity as owner of the measurement station, is responsible for its management and maintenance as well as all other activities related to the measurement process (data acquisition and validation, forwarding to Snam Rete Gas in order to account for the gas inserted into the network and archiving for the purposes of current tax and administrative laws). 3.2) System for measuring the volume of gas inserted into the network The measurement station consists of two separate lines arranged in parallel, each with its own meter of Qmax 10,000 m 3 /h to measure the maximum expected load of gas in transit. The lines can be configured in series for control purposes. The measurement lines, equipment performance and system configuration are designed to meet legal requirements and national and international standards. The station was built with the following conditions: maximum hourly station capacity 600,000 Sm 3 /h; working pressure of between 22 and 72 bars. The volume is determined by means of two meters, one intended as a "primary measurement" and the other intended as a "reserve and control measurement (backup)." The type and characteristics of the meters installed are as follows: the primary measurement consists of a turbine meter which is constructed, installed and operated in compliance with standards UNI 7988 and ISO 9951 and the EEC Directive; the counter also bears the "verified first" stamp and has been tested on the testbench at a pressure of 60 bars. the reserve and control measurement (back-up) performed by means of an ultrasonic meter installed in accordance with standard ISO 9951; the meter was tested on the testbench at a pressure of 60. The recommended range of use of meters is between 10% and 90% of Qmax of the meter; in the event that the volumes exceed the maximum load of a meter, the two measurement lines can be opened simultaneously. The measurement pressure and temperature are detected by means of special transmitters, in particular, the pressure is detected on the appropriate reader on the meter body while the temperature sensor is inserted 5 DN downstream of the same. On each measurement line, close to the primary element, there are specific outlets to connect equipment required to carry out on-line checks in parallel with the main measurement system. 11-5

6 3.3) Checking of instruments Checks on the measurement instruments are performed in accordance with the procedures described in the chapter entitled "Quality of the LNG delivered and the gas redelivered". 3.4) Consumption and losses The amount of regasified LNG redelivered by the Operator to the User at the Redelivery Point (expressed in MJ), shall correspond to the volume of LNG delivered by the User to the Operator, less consumption and losses at the Panigaglia Terminal: a fee in kind equal to a percentage of the quantity of LNG delivered, defined by the Regulatory Authority as part of the verification of the rates proposed by the regasification enterprise, shall be paid by the User to cover consumption and losses associated with the regasification process. 11-6