DIGESTER AIR-TIGHTNESS TESTS

Transcription

1 PE-GC-001D 1/9 DIGESTER AIR-TIGHTNESS TESTS Content 1. FOREWORD 2 2. THE ACTORS 2 3. TESTS AND PRELIMINARY STATEMENT OF WORKS 3 4. EQUIPMENT REQUIRED FOR THE AIR-TIGHTNESS TEST 4 5. DESCRIPTION OF THE CLEAN WATER FILL AIR PRESSURISATION SPRAYING THE DOME WITH SOAPY WATER VISUAL CHECK Test Test LOCATING LEAKS FOUND AND REMEDIAL WORK Locating leaks Remedial works REPEATED AIR-TIGHTNESS TEST 7 6. SUBSEQUENT WORKS 8 7. PLANNING - QAP 8 8. AIR TEST FORM 8

2 PE-GC-001 D 2 / 9 1. FOREWORD The present document shall be read with specifications Y1400 Anaerobic Digesteur Design and Construction, and 1405 Anaerobic digester, internal coating. Biogas confined in the upper section of a digester, by virtue of its aggressive properties*, causes serious and rapid deterioration of concrete, the material constituting the tank s main structure. In order to obtain gas tightness of the structure and eliminate any contact between the biogas and the concrete and thus eliminate the danger of damage to this structure, a protective coating is applied to the inner surfaces of the digester enclosing this biogas**. By virtue of its function and of the guarantee required***, this coating must provide a sealed barrier against the biogas and not merely an «impermeable coating» even in the event of micro-fissures. The purpose of this procedure consists in testing the gas tightness of the concrete structure before coating and then checking it after coating of relevant under pressure conditions that are equivalent to those prevailing during the structure s operating phase. * - mixture of methane (CH 4) carbon dioxide (CO 2) carbon monoxide (CO), hydrogen sulphide (H 2S), nitrogen (N 2) and hydrogen (H 2) among others. - operating temperature of between 8 and 40 C. - water vapour saturated medium - approximately 40 mbar overpressure - approximately - 20 mbar vacuum ** dome lower surface and part of the cylindrical skirt up to 1.00 m below the lowest hydraulic level *** 5 or 10-years guarantee (according to contractual conditions) on biogas-tightness and satisfactory resistance to aggressive agents generated by its composition 2. THE ACTORS The following parties participate in air-tightness tests: «the Supplier» The company that has designed, recommended and supplied the products constituting the protective and sealing coating. «the Applier» A specialist company that has been approved by the Supplier and that is responsible for applying the biogas protection and sealing coating; this company will usually be working as a subcontractor for the Civil Engineering company responsible for constructing the digester. «the Contractor» The Civil Engineering contractor responsible for constructing the civil engineering part of the digester including the coatings subject of the tests in this procedure. The contractor may act as a subcontractor or co-contractor to Degrémont. «Degrémont» Involved as: - either the general contractor with regard to the Client in the case of a civil engineering subcontractor, - or as the Client s authorized representative in the case of a civil engineering co-contractor, Propriété DEGREMONT - Reproduction Interdite Date de création : juin 1995 Date de modification : December Indice D

3 PE-GC-001 D 3 / 9 «the Consultant» Organization entrusted by the Client with the task of supervising the works, «the Client» Public or private entity responsible for awarding the main works contract, The Contractor is exclusively responsible to Degrémont for work carried out by the Supplier and the Applier. Accordingly, all documents on digester gas-tightness tests (mail, notes and technical bulletins, reports etc.), regardless of their origin, must be submitted in the name of the general Contractor and on its letter heading. All work on the structure relating to sealing tests MUST be carried out in the presence of a representative from each of the following: - the applicator (and the Supplier depending on requirements) - the general Contractor - Degrémont - the Consultant (and from the Client if the latter so wishes) Upon completion of these works, the report drafted by the general Contractor must be signed by these representatives. 3. TESTS AND PRELIMINARY STATEMENT OF WORKS 2 sets of pressurization tests will be achieved : - Test 1 : before any coating of the concrete to be protected but after the preliminary surface preparation. The aim is to localize the main concrete cracks of the dome for injecting them. - Test 2 : after the protective coating has been applied according to specification Y1405 and after the satisfactory contradictory statement of coating control further to specification Y1250. The aim is to test the compliance of the structure with the nominal pressure as well as the gas tightness of the protective coating. Under no circumstances will the report delivered on completion of the visual check constitute an acceptance report, albeit partial, for the coating applied. The exclusive purpose of this document consists in checking that the product has been used without generating any apparent anomaly. It is compulsory for the actual air-tightness test to be carried out in the following working configuration: - After all the connectors crossing through the walls affected by the biogas volume have been fitted and anchored, excluding any other equipment components. Pipes shall be closed and tightened by steel plates, - After temporarily blanking off all openings into the biogas area such as connectors, sampling outlets, manhole covers etc. Special care must be taken with these temporary blanking arrangements in order to ensure that they are totally air-sealed (the use of a continuous flexible seal or any other process that will guarantee the level of sealing required) and thus achieve test optimization with regard to the coating itself, ensuring that there are no unwarranted leaks that could affect the satisfactory outcome of the tests. - Outer surface of the bare dome, visible concrete, before applying the external sealing and thermal insulation layer. No product shall be applied over the concrete before the success of the present tightness tests. - Outer surface of the bare digester wall, visible concrete, before applying the thermal insulation layer and its protection, - Arrangements providing protection against falls and implemented on the dome in order to ensure operative safety during the test,

4 PE-GC-001 D 4 / 9 - Structure waterproofing according to contractual requirements, relevant testing completed and conformity report signed by Degrémont and the Consultant, according to the Degrémont procedure PE-GC-002. The digester s air-tightness test is undertaken with the structure filled with water and the gas space compressed; consequently, satisfactory waterproofing is mandatory in order to avoid any impact on testing. - The structure must be filled with water up to the level where the protective coatings ends + 20 cm. According to specification Y1405, the protective coating ends 1m below the sludges minimum level. 4. EQUIPMENT REQUIRED FOR THE AIR-TIGHTNESS TEST Specific equipment needs to be put in place for this test; see below for the basic configuration of the various components. The manhole located on the top of the dome must be temporarily closed using a 5 mm thick metal sheet. Bolts are used to fix this sheet to the frame anchored in the concrete structure. A continuous mastic seal is used to ensure that the assembly is sealed. Four pipes are connected to the internal air space through the temporary closing metal sheets. To these openings are coupled : - a low pressure manometer, preferably a water manometer - a pressure relief valve set at design pressure +5 mbars, by default 45 mbars for pressure test. This valve can be replaced byan hydraulic protection for the safety of the dome - a compressed air supply connected to a compressor delivering a 6 bar pressure. - A thermometer measuring the temperature of the internal air space 0 to 100 mbar pressure gauge Pressure relief valve set to 45 mbar Check valve Compressor inlet Pressure relief valve Pressuring the air space above the liquor under the dome The compressed air supply is equipped with a by-pass fitted with a pressure relief valve thus ensuring that the air under the dome is compressed in complete safety.

5 PE-GC-001 D 5 / 9 5. DESCRIPTION OF THE 5.1 Clean water fill If the structure has been drained after sealing tests, it must be filled with clean water up to the end level of the coating + 20 cm as described here above in chapter 3. If the structure has been partially filled with water beforehand, the water level is topped up until it reaches this highest level In case of first filling, it shall be done according to the filling procedure used for water tests (steps of approximately 1 m of water per day). Otherwise the structure can be filled with steps of 3 m per day and the last meter will be filled within 24h. 5.2 Air pressurisation The gas volume confined in the top part of the digester must be inflated with air at the design pressure, by default 40 mbar, with a step at +30 mbar using the mechanism described in paragraph 4. The test is processed according to the following specifications 5.3 to 5.5. This stepped filling procedure is required to ensure that the dome is pressurized gradually. These intervals will be established by the structure s designer drawing office (approximately 10 mbar per hour), 5.3 Spraying the dome with soapy water The bare concrete of the dome s outer surface and its upper hoop are sprayed with a mixture of water and Teepol type surfactant liquid soap or other similar product. Remember that comprehensive collective safety measures must be put in place throughout the procedure. 5.4 Visual check The conformity report is subject to a contradictory statement according to the standard form enclosed at the end of the present document Test 1 After the soapy water spray, a visual check of all sprayed surfaced (surface of the dome as well as the upper part of the walls corresponding to the internal air space) is achieved : zones of important (surface bigger than 100 cm², thickness greater than 2cm) bubbling are marked in order to repair by injection all related concrete cracks. Product and injection procedure are subject to Degrémont s and Applier s approval. Bubbling examples

6 PE-GC-001 D 6 / Test 2 After spraying the soapy water, an accurate visual check is carried out on all surfaces that have been sprayed (dome outer surface and upper part of walls): - Results case 1: When there are no bubbles, however small, at any point and pressure has been maintained for at least one hour, the air-tightness test can be deemed successful. Bubbling example Maintaining pressure shall be understood as pressure decrease less than 0.25% in 1h or less than 5% in 24h, at constant temperature. In case of temperature variation, the pressure shall be corrected further to the equation P 2 = P 1 x T 2 / T 1 (be careful in expressing the temperature in K : T(K) = T( C) ). If the sun shines t oo much on the dome, the test shall be performed at night. A structure s air-tightness test sheet* is then signed by representatives of the Consultant, Degrémont and the Contractor respectively. *along the lines of the document featured in the appendix.

7 PE-GC-001 D 7 / 9 - Results case 2: The pressure is not maintained for at least one hour or bubbles appear. These bubbles show up where air is leaking through the dome. The sealing test is deemed unsuccessful. Once the anomalies have been pinpointed with an electrical comb, the coating must be repaired. An air-tightness test sheet is prepared for the structure further to the enclosed standard form and marked «non conformity».this test sheet details the number and nature of the anomalies found together with the requisite remedial work. It is then signed by representatives of the Consultant, Degrémont, the Applier and the Contractor respectively. 5.5 Locating leaks found and remedial work Locating leaks Leaks must accurately marked on the outer concrete surface of the dome using an indelible product; they must also be marked at the same time on a digester roof drawing. Coating defaults will be searched with an electrical comb after emptying of the digester. They will be located on the relevant drawing. The most suitable medium for the latter record is still the digester dome shuttering drawing or the drawing showing the roofing permanent shuttering concrete slabs when the prefabricated system is selected. When the document has been completed, it is given a new name, numbered and attached to the «non conformity» sheet raised on completion of the visual check procedure Remedial works As the internal coating applied beneath the dome and to the upper section of digester's shell is entirely responsible for ensuring a air tightness, any remedial work undertaken to reinstate this function s compliance must be undertaken from the inside of the structure, on the product itself. If, however, work is required to individual points on the external layer of the dome s concrete structure as the result of any anomaly found during the visual check procedure, this work must never replace remedial work to the sealing coating itself inside the dome. In any case, this surface work must be regarded as entirely exceptional; the condition of the dome s concrete (internal and external) is assumed to be conform and to have been acceptance tested by the applicator before applying the sealing coating. Work carried out on the coating must be covered by a «detailed works technical document» prepared by the applicator and forwarded for information for and on behalf of the Contractor, to the Consultant and to Degrémont. In particular, this document must detail the type of work considered (breaching the coating at certain points, bridging, glass yarn reinforcement layer, additional coating etc.), any provisions required prior to commencing the work (draining the structure, special scaffolding requirements*, nacelle etc.) together with a detailed schedule and operations log. * It is recommended for scaffolding erected for the purpose of coating application to be left in place throughout the hydraulic test and the air test so that action can be taken quickly should a repair be required. It is compulsory for the technical works document to be signed off «without comments» from the Consultant and Degrémont before commencing the works concerned. Remember that no comments expressed by the Consultant or Degrémont on this document and no signatures can, in any event, diminish the general contractor s responsibility which remains total as far as the work is concerned. 5.6 Repeated air-tightness test Once remedial work has been completed, a further gas-tightness test procedure is carried out according to the provisions specified in paragraph 5.

8 PE-GC-001 D 8 / 9 This procedure is repeated as often as necessary until the test is successful. 6. SUBSEQUENT WORKS Once the air-tightness test sheet on the structure has been signed by the respective representatives of the Consultant, Degrémont and the general contractor, the latter gradually drains out the structure in order to avoid any sudden stress to the digester structure. Work can then commence on installing the digester s electromechanical equipment and also on additional civil engineering works (thermal insulation and sealing arrangement on the dome, thermal insulation and protection on the outside of the shell, etc.) 7. PLANNING - QAP All works involved in digester air-tightness tests must be allowed for in the general works programme prepared by the general contractor. Additionally, it is compulsory for these works to be covered by a specific QAP (quality assurance programme) which must also be prepared by the general contractor before digester construction work commences. 8. AIR TEST FORM Refer to next page

9 PE-GC-001 D 9 / 9 D I G E S T E R A I R T I G H T N E S S T E S T Project : Date : Degrémont represented by : Contractor : Applier : Supplier : Client : Consultant Concerned structure : According to Degrémont specification Y1250 shall be joined to this form the two successful reception form of the internal coating of the digester. Absence of bubbling (no bubble admitted) : Yes No Control of pressure maintain : Start of test End of test Hour Temperature Corrected pressure with T( K) = T( C) P 2 = P 1 x T 2 / T 1 Pressure Difference of pressure less than 0.25% over 1h or 5% over 24h : Yes No Conclusion : Test conformity : Yes No