104 m³ Explosion-Proof Chemical Cold Storage Project in Jiaxing

Project Background

Zhejiang Xinyu Trading Co., Ltd. specializes in the storage, transportation and distribution of chemical raw materials such as acrylic resins, polyurethane curing agents and diluents for coatings, with its products widely supplied to local automotive refinish and industrial coating manufacturers across Zhejiang. For some polymer-grade isocyanates and peroxide initiators stored at its chemical logistics center, their Material Safety Data Sheets (MSDS) explicitly specify a maximum storage temperature of -5°C, with strict separation from heat and ignition sources.

Previously, the company adopted a makeshift solution of retrofitting an ordinary third-party cold storage with split explosion-proof air conditioners. The warehouse lacked an integrated explosion-proof zoning design and suffered poor temperature uniformity. Temperature probe records showed the highest indoor temperature could reach -3°C in summer while edge areas dropped to only -8°C. Additionally, non-explosion-proof lighting fixtures and sockets inside the warehouse created severe non-compliance safety hazards.

Following an on-site inspection in October 2023, the Jiashan Emergency Management Bureau issued a rectification order mandating the construction of a standalone explosion-proof cold storage, which must be interlocked with the base’s flammable gas alarm system. In response, Xinyu resolved to build a small dedicated explosion-proof cold storage within its own logistics base for constant -10°C storage of Category A hazardous materials. Beyond meeting regulatory requirements, the facility was required to connect to the existing Warehouse Management System (WMS) to enable unattended automatic temperature control during goods warehousing.

Key Challenges

Challenge 1: Matching refrigeration equipment with gas explosion-proof classification

Vapors volatilized from stored materials mainly consist of butyl acetate, xylene and trace isocyanates. Per hazardous area classification standards, this environment falls under Zone 2, Gas Group IIB, Ignition Temperature Group T4. All electrical components of the refrigeration system—compressors, condenser fan motors, evaporator fan motors, defrost heating tubes and all auxiliary electrical accessories—must hold complete explosion-proof certification with a marking no lower than Ex d IIB T4 or Ex p IIB T4.

Off-the-shelf small air-cooled scroll units that simultaneously meet IIB T4 explosion-proof rating and -10°C evaporation temperature requirements are scarce on the market. Most manufacturers require a customization lead time of over 45 days, while the client only had a 60-day rectification deadline.

Challenge 2: Temperature field control within confined space

The cold storage has internal dimensions of 7.4 m (length) × 4.8 m (width) × 2.9 m (height), with an effective volume of merely 104 m³. Three layers of pallet racking are installed inside for high cargo turnover, requiring full warehouse door openings for loading and unloading at least twice daily. Dense storage in a compact space easily blocks cold air return passages, potentially creating a front-to-rear temperature difference exceeding 4°C inside the warehouse. Per material storage requirements, temperatures at all storage positions must stay within -10°C ±2°C; any deviation triggers audible and visual alarms and interlocks to cut off refrigerant supply to the refrigeration system.

Challenge 3: Dual requirements for floor thermal insulation and load bearing

Reach stackers are used for pallet loading and unloading inside the warehouse, with a combined weight of the forklift and loaded cargo exceeding 2.5 tons. Polyurethane wall panels cannot withstand long-term wheel loads. The floor slab must achieve a thermal resistance of R ≥5.0 m²·K/W while satisfying concentrated point load requirements.

Conventional cold storage floors adopt XPS insulation boards topped with reinforced concrete, yet the site’s original plain concrete floor only permits an overall elevation increase of 200 mm. Precise thickness allocation between the 150 mm XPS layer and 100 mm reinforced concrete layer was required. Structural measures were also implemented to resist shear slippage at the interface between XPS and reinforced concrete, preventing uneven compression of XPS under heavy loads that would crack the floor slab.

Challenge 4: Ventilation and flammable gas detection interlock logic

Flammable gas may accumulate inside the explosion-proof cold storage in the event of refrigerant leakage or damaged material packaging. Per design codes, fixed flammable gas detectors must be installed with two-stage alarm logic: the first alarm activates explosion-proof exhaust fans for forced ventilation, while the second alarm cuts off power to all non-intrinsically safe circuits inside the warehouse.

However, catalytic bead sensors suffer degraded response accuracy and shortened service life under -10°C low-temperature conditions. Infrared or cryogenic-resistant detectors were therefore selected. Special design measures also eliminated false triggering of sensors by water droplets generated during evaporator defrost cycles.